1. Church Reef, in Wembury Bay, near Plymouth, was selected for a survey of common intertidal plants and animals.

2. Four traverses were accurately levelled relative to Ordnance Datum, and their floras and faunas examined.

3. The relation between predicted tide levels and probable actual levels is discussed, and the importance of the “splash zone” is stressed.

4. As an outcome of 2 and 3, it appears that on Church Reef the most critical levels on the shore, for the species examined, are: (a) between Mean and Extreme Low Water Springs; (b) between Mean Low Water Neaps and Springs; (c) at Extreme (Lowest) High Water Neaps. The least critical level is Mean Low Water Neaps.

5. Two special problems are presented by the upper limits of Littorina saxatilis and L. neritoides, and by the frontiers between Ascophyllum and Fucus spiralis and between F. spiralis and Pelvetia, where the algæ do not overlap.

6. The work of previous authors is discussed for comparison with the present paper.

7. An important difference is suggested between the nature of the zonation of sedentary animals and plants on the one hand, and that of animals capable of locomotion on the other hand.

The two forms of Trivia which are recorded from Plymouth (Marine Biological Association, 1931) have hitherto been regarded as one species (Trivia europea), but recent researches (Peile, 1925; Pelseneer, 1932) have shown them to be distinct. Peile calls the two species Trivia monacha (Da Costa), with the spotted shell, and Trivia arctica (Montagu), with the unspotted shell. Pelseneer calls them respectively Cyprœa (Trivia) europœa L. and Cyprœa (Trivia) arctica Montagu. A closer investigation at Plymouth fully bears out the conclusion of the above-mentioned workers that there are two species and the fact, brought forward for the first time in the present paper, that the larvæ are also distinct makes the determination doubly sure.

Nothing is known of the life-history of Erato voluta (Montagu)=Erato lævis (Donovan) and in the following note the larvæ are described for the first time. Erato being very closely related to Trivia, it was to be expected that the larvæ would be somewhat similar, but, although there is here, as in Trivia, an Echinospira larva, the details of its life-history are quite different and the accessory shell when fully developed differs much from that of Trivia.

The life-histories of the two species of Cerithiopsis are described here for the first time, that of Triphora perversa is partly known already. All three species are common in Plymouth and their larvæ are very common in the plankton in spring and summer. Pelseneer (1926) has described the eggs and newly-hatched larvæ of Triphora perversa from the Brittany coast and Fischer (1884) has noted that it has a very long free-swimming life, still being a veliger with up to 7 or 8 whorls. The eggs of Cerithiopsis barleei have now been found at Plymouth and the larvæ reared as far as a stage just before settling down, the late stages from the plankton being reared to the crawling stage in plunger-jar. The eggs of Cerithiopsis tubercularis have not yet been seen, but the larvæ are common in the plankton and the late larvæ have also been reared in a plunger-jar until the crawling stage.

Nothing is known of the eggs and larvæ of Turritella communis and, except for the young shells which have already metamorphosed, those of Aporrhais pes-pelicani are also unknown. The following descriptions are therefore new, both molluscs having been kept in plunger-jars until they laid their eggs.

The genus Philbertia, belonging to the family Turridæ, is well known to have the larval shell beautifully sculptured and, as it is retained as the apex of the adult shell instead of being knocked off or concealed as is the case with many gastropods, it is easy to identify as belonging to this group, the veligers also reaching a large size and being conspicuous in the plankton.

1. Artificial fertilisations of Notomastus latericeus Sars were made and the larvæ reared.

2. The two-day old trochosphere is provided with a large central mass of yolk. It has a broad prototroch, a telotroch, a neurotroch and an apical tuft. It swims rapidly.

3. Development consists in the appearance of trunk segments; The most anterior of these is the achætous peristomium. Those following acquire neuro- and notopodial chætæ.

4. At an age of about ten days the cilia are gradually lost. The larva then has about five chætigerous segments, the first three bearing bristles, the last two hooded hooks.

5. The young worms lived for some twelve days after metamorphosis and by that time had seven clætigerous segments. Only a little of the yolk still remained. The worms possessed a protrusible introvert and were feeding on diatoms.

6. The larva apart from its strong prototroch and rapidity of swimming does not exhibit any special structural adaptations to pelagic life, such as are found in some other Polychæte larvæ. In comparison with Capitella it has fewer segments when it metamorphoses.

The Notodelphoidea are a heterogeneous collection of copepods which are found parasitic within urochordates and there is considerable doubt as to the exact systematic position which should be occupied by this group. It comprises—in the sense in which it is used by Sars (1921)—six families of excessively doubtful affinities in that there are grouped together Copepods (1) which brood their eggs (Notodelphys, Doropygus, etc.), (2) others which are possessed of elongate egg-strings (Entericola), (3) and others which deposit their eggs singly (Mycophilus). Now it appears to the present writer that such great variation in habit must argue an equally great variation in the structure of the genital organs, for the “cement gland” and “hardening gland” (see Gray, 1928) may be presumed to be absent if egg-strings are not formed. It is doubtful, therefore, whether any useful discussion on the classification of these forms can take place without a parallel and detailed investigation of the internal anatomy. There is, however, another line of approach—the study of larval forms. It is equally as a preliminary skirmish along this line of attack, and as a contribution to our knowledge of larval forms, that the present brief note is presented.

The notodelphoid copepods parasitic within Ascidians have been generally ignored for a long time. In May 1932 the present writer collected a considerable number at Millport Marine Biological Station, and was amazed at the frequency with which they occur. It may be that the Clyde area is especially favourable to their development, or it may be that the season was particularly good, for about thirty specimens were collected of ten species, of which at least one—the subject of the present paper—was new to science. If this abundance of forms is indeed usual, it is difficult to understand why records are not more frequent, and it would be interesting to learn how frequently these fascinating and aberrant forms are lost in the course of class dissections of their hosts.

In recent years the development stages of Copepoda have been the subject of study by various workers. Their attention, however, has been mainly directed to fresh-water species, presumably because the material is more readily available, and it seems desirable that our knowledge of the development of marine Copepoda should be extended. The material utilised for the present work was collected on the periodic and comprehensive fishery cruises carried out by the F.B.S. Explorer, and we are indebted to the Fishery Board for Scotland for permission to undertake this detailed study. Since the appearance of Grobben's standard work on Cetochilus septentrionalis Goodsir (Calanus finmarchicus Gunn.), the only important publication dealing with the life-histories of marine Copepoda, so far as we have been able to ascertain, is that of Oberg, who, in Die Metamorphose der Plankton-Copepoden der Kieler Buclit, describes the development stages of seven common marine forms. Oberg's choice of species, which are all more or less neritic, was again obviously dictated to him by the material at his disposal, and it is hoped that our collections, which cover not only the northern part of the North Sea, but also the Faroe–Shetland Channel, and part of the Atlantic itself, will furnish material for the establishment of the life-histories of some of the more oceanic forms.

During my researches on the vertical and seasonal distribution of young fishes I soon noticed that occasionally a specimen was found to which a Caligid copepod in an early chalimus stage was attached. As every fish caught was examined under the lens while being measured, I kept a look out for these young stages of the parasites and all occurrences were recorded. The results of this examination are given in Table I which shows also the lengths in millimetres of all the fish thus parasitised found in the collections made during 1925 and 1926 (see 1, 2, 3 and 4).

In a previous paper an account was given of the breeding and growth of Sagitta setosa throughout a year (2). The results appeared to show that the last spawning took place in October and the resulting offspring lived through November and December without maturing and that by February there were indications that a number were spawning. At the end of the following April and beginning of May a complete spawning population was formed. Owing to the large size at which these matured it was assumed (2, p. 148) that they had been the offspring of adults spawning in February. The true trend of events was however by no means clear as the increase in average size from January to May was very even (2, Plate II). There was a distinct difference at this period between S. elegans and S. setosa. In S. elegans a spawning population of individuals all about the same length was produced in February which apparently gave rise to a brood which had grown to a large size by April and May, and the change in size from February to May was much more abrupt than in S. setosa (1, Plate I). It was clear that while the February curve for S. elegans showed very little variation in size for the majority of the population caught, the population in May tended to be very widely dispersed. In S. setosa, on the other hand, there was a gradual narrowing down of the dispersion until a spawning population with little variation in length was produced by May.

1. Observations are given on the vertical distribution of Sagitta elegans and S. setosa in the daytime.

2. An account is given of the seasonal abundance of both species of Sagitta throughout the year as shown by collections made with oblique hauls with the 2-metre stramin ring-trawl and hauls with a bottom plankton net.

3. An attempt is made to piece together as much as possible of the life-stories and habits of Sagitta in offshore waters off Plymouth on the basis of these and previous observations.

One hundred and twenty-one specimens of Calanus finmarchicus were anæsthetised in a dilute solution of Urethane (2·5 grms. in 100 c.c. of seawater) and the time taken by each to sink through a measured distance determined. The length of each specimen, in millimetres, was noted, and the relationship between sinking time and length of the individual was determined. The coefficient of correlation, r, was found to be —0·63.

Apstein (1910, p. 23), working with preserved material, found that the time taken by adult Calanus was less than that taken by young. He does not give actual length measurements. Eyden (1923, p. 53) showed that for anaesthetised specimens of Daphnia pulex, the average rate of fall was approximately twice as great in specimens of length 2·5–3·0 mm. as in smaller ones, whose length varied from 1·5–2·0 mm.

The position in which specimens sank was conditioned by the manner in which the antennæ were held. It was found, however, that this had not as great an influence on the sinking rate as might have been expected.

Of the 121 specimens examined, 21 were in Stage IV, 41 in Stage V; 59 were adult, of which 54 were females and only 5 were males.

The belief for long was held by early investigators that among most if not among all Elasmobranch fishes the number of females in the stocks exceeded that of the males. As long ago as 1884 Day (4, p. 345) remarked concerning the Thornback Ray, Raia clavata, “It has been said that the number of females is in excess of that of the males.” Haacke (9, p. 246), writing in 1885, says of the Sharks and Rays which he had observed in South Australian waters, “Bei den südaustralischen Haien und Rochen, auf deren Fang ich zu wiederholten Malen ausgezogen bin und von denen mir auch nicht selten Exemplare für das Adelaider Museum zugeschickt wurden, habe ich die Wahrnehmung gemacht, dass Männchen verhältnismässig sehr selten gefangen werden. Ob diese Wahrnehmung auch anderswo gemacht worden ist, weiss ich nicht, jedoch ist es nicht unwahrscheinlich; in der mir zu Gebote stehenden Litteratur finde ich nichts darüber. Die seltenheit der geschlechtsreifen Männchen, soweit sie sich wenigstens durch die Fangresultate dokumentiert, gilt für sämtliche Species der ziemlich artenreichen südaustralischen Selachierfauna.”

Records of parasitic worms from British marine fishes are still rather scanty. A good deal of attention has been paid to the subject of the Trernatodes by Nicoll, whose valuable list (1915) is indispensable to anyone working in this field. Nicoll is himself responsible for the records of the majority of the 49 species of Trematodes given in the second edition (1931) of the “Plymouth Marine Fauna.” The only work done on the Cestodes of fishes at Plymouth appears to have been that of Woodland (1927, a and b), as a result of which 14 species have been placed on record. Very few data are available as to the Nematodes, and none as to the Acanthocephala, of the Plymouth fauna.

It is only occasionally that pelagic tunicates of the genera Doliolum and Salpa are recorded in numbers in the waters off Plymouth. In view of their possible use as indicators of the presence of Atlantic water (see Bowman, 1923; and Schmidt, 1909, p. 159), it is of value that their occurrence should be put on record. Regular weekly catches of plankton have been made since 1930 with half-hour oblique hauls with the two-metre stramin ring-trawl. During this period species of both genera have appeared in such numbers that it has seemed desirable to make a careful examination of the species occurring.

This Autolytus has been known only in the form of Sacconereis, i.e. as the female stolon of an unknown Syllid. It was discovered in 1864 by a French zoologist, E. Claparède, at Port-Vendres (Pyrénées Orientales). According to the original figures and description it is an ordinary female individual in its general appearance, carrying a large egg-sac on the ventral side. The latter is “étranglé en 8” and turkish blue, the colour being due to the contained eggs. The body consists of about 60 segments, the dorsal surface of which is transversely banded by pigment of rose colour. Modification of the segments for swimming commences at the 9th setigerous segment and stops at the 21st. The following 40 segments (about) are not modified like the 8 in the first region just behind the head. The most striking character, by which the present stolon is distinguished from any other Sacconereis, is the presence of a pair of extra appendages in front of the head in addition to the median and lateral tentacles. Claparède states that the presence of these appendages, “qui n”ont été signalés chez aucune autre Sacconereide,” is by no means very astonishing, since there are two such ones in Polybostricus. Claparède clearly predicted their homology to the frontal lobes of the bifid antenna-like appendages in the male head. A. Malaquin (1893) actually explained the bifid condition of the frontal appendages of the male as due to their origin in the fusion of the lateral tentacles and the palpi.

(1) The asymmetrical development in Hydroides opercula is due to the growth difference between two sides in the same kind of organs. The presence of a functional organ holds its mate in check. Therefore, taking off the functional operculum results in the development of the rudimentary side.

(2) This phenomenon of compensatory regulation cannot be considered to be brought about by a nervous reflex set in motion by the stimulation of damaged nerves in the operated operculum, since, for example, the inhibitory influence to a certain extent depends on the degrees of injury.

(3) It is also not proved to be due to the production of a certain chemical substance which stimulates the rudimentary organ to grow, while the wound itself affects directly the inhibitory action of the functional operculum.

(4) The inhibitory influence is only localized in the operculum and not outside of it. Therefore, cutting off the gill filaments or other parts of the body does not bring a reversal of asymmetry.

(5) Within the limit of the operculum there is no special centre of the inhibitory influence, which depends on the intactness of the internal constitution of the organ. Those peripheral parts outside the limit of direct blood supply can be cut off, without the resulting reversal of asymmetry. A simple puncturing with a fine needle also has no effect. But greater injury accompanied by an outflow of blood always starts the rudimentary organ developing.

(6) The functional operculurn has no regenerative capacity, while the rudimentary one still has. The injured operculum is thrown off sooner or later from the body, and a new start repeats from the beginning the original development. By accelerating this regenerative development of the old functional organ, or properly controlling the growth of the rudimentary organ on the opposite side, a symmetrical animal with two large opercula can easily be derived. On the other hand, if both rudiments antagonistically check each other's development, a symmetrical animal with two small rudimentary opercula is produced.

(7) Since, however, either the right or the left or even both rudiments can be made to develop into a functional organ, the inhibitory influence must act at first on both alike, unless a threshold value is assumed. In the present species of Polychsete it is as a rule the right-handed one that grows more quickly than the other.

(8) With regard to the nature of the asymmetry in Hydroides it seems to be quite different from that in the male Gelasimus in which the asymmetry of the chelas is said to be derived from the symmetrical condition relatively late in development, and the relation, once attained, becomes fixed.

(9) In Hydroides norvegica at least, the opercula show a tendency to right-handed growth from the beginning of their development, but this condition of asymmetry is very unstable and is easily reversible by an external influence even in the adult state, i.e. there is no critical stage at which it is irreversibly determined.

1. The changes brought about in the colour of the gills of rainbow trout and sea trout smolts by various poisons are described.

2. Cyanide causes a marked brightening, whilst phenolic substances, dissolved oxygen deficiency and naphthalene bring about a darkening of the gill colour. Fresh, untreated sewage has no effect.

3. The gill colour of smolts dying in the Tees Estuary was brighter than normal, indicating cyanide poisoning. This conclusion was confirmed by chemical methods.