Two nucleoproteins with similar chemical composition have been isolated from the leaves of tobacco plants infected with tobacco necrosis virus. One of these is crystalline and has a sedimentation constant of 130 × 10−13; the other is amorphous and its principal component has a sedimentation constant of 58 × lO−13.

Each preparation will infect plants at a dilution of 1 in 108 and will precipitate specifically with antiserum at a dilution of 1 in 3·2 × 105.

The nature of the difference between preparations in the two states is obscure and it has not proved possible to convert the one into the other.

Echinorhynchus gadi (Zoega) Müller has been found parasitic in various species of Pacific salmon. The amphipod Cyphocaris challengeri Stebbing serves as an intermediary host for this parasite in the region in which the investigations were carried out.

Echinorhynchus lageniformis sp.nov. and Corynosoma strumosum (Rudolphi) both parasitic in the Starry flounder (Platichthys stellatus (Pallas)) and the Two-lined flounder (Lepidopsetta bilineata (Ayres)) are recorded with data on their occurrence.

One hundred and ninety-seven English sparrows collected in the vicinity of Lafayette, Indiana, have been examined for cestode parasites. The species recovered and incidences of infection are as follows: Hymenolepis passeris (Gmelin), 2·5%; Choanotaenia passerina (Fuhrmann) provis, 3·5%; Anonchotaenia globata (von Linstow), 2·5%. Of these, Hymenolepis passeris is reported for the first time from North America. The name Haploparaxis linstowi is proposed for Aploparaksis fringillarum von Linstow nec Rudolphi. Additions are made to the present descriptions of the species observed.

The purpose of this work has been to identify and describe the immature forms of those species of tachinids which have occurred as parasites of Pierisrapae and P. brassicae at the Imperial College Field Station, Slough, Bucks.

This paper deals with the species of the commonest genus of the American Streblidae. The descriptions of the species were made from specimens mounted on slides, in Canada balsam. Here I wish to point out again that spirit preserved specimens are unsuitable for the study of these Diptera. These specimens do not show clearly the details of the structure of some sclerotized parts, and especially the arrangement of the small setae on the thorax, which in some cases, are the only reliable characters for the separation of the species. The study of unmounted specimens of these Diptera may easily lead to incorrect identification, or to the increase of undesirable synonyms.

The following animals are from a collection made for and kindly presented to me by Miss Nora G. Sproston during her visit to the Station Biologique de Roscoff, Finistère, in June 1937.

Experiments upon the duration of chronic infections of Plasmodium relictum in canaries prove that parasites may persist in the peripheral blood, as ordinary schizogonic stages, up to 8 years and 3 months after infection and that the blood of such birds is infective for clean birds for at least the same period.

In Plasmodium gallinaceum, parasitic in domestic fowls, in addition to the schizogony in red blood corpuscles, schizogony also occurs in monocytes and cells of the reticulo-endothelial system. This schizogony in cells other than erythrocytes may be termed, for convenience, exo-erythrocytic schizogony.

Exo-erythrocytic schizonts are characterized by never having malarial pigment (as they live in cells devoid of haemoglobin), by growing to a large size and forming numerous merozoites, up to 50 or 60 or even more.

Exo-erythrocytic schizonts are not confined to leucocytes of the blood stream, but can also develop in fixed endothelial cells of organs such as the brain, lung, liver and spleen.

The brain is an especially important focus of development and, after sporozoite infection, it is the first organ in which exo-erythrocytic schizonts develop. These schizonts may be found in capillaries of the brain as soon as parasitized erythrocytes are present in the peripheral circulation, but as yet they have not been found before parasites-are present in the peripheral blood.

In the brain rows of schizonts may develop and ultimately occlude most of the capillaries in the brain. This blockage of capillaries results in symptoms of general paralysis in the infected birds and death follows in a few days; and it frequently occurs in birds which apparently have been cured of the peripheral infection by treatment with quinine.

The exo-erythrocytic stages of P. gallinaceum occur in birds which have been inoculated with blood or with sporozoites.

During growth, the body of the schizont breaks up into a number of masses or cytomeres, on the periphery of which the merozoites are developed on regularly arranged rows of digitiform processes. A mass of chromatin migrates to the distal end of each process and is cut off to form a merozoite.

The mature schizont consists of a mass of irregular merozoites enclosed in a sac-like membrane which may be the remains of the host cell. The merozoites are composed almost entirely of chromatin and when they are fully developed practically no cytoplasm of the schizont remains.

1. Diapause in Lucilia sericata is caused by unfavourable conditions during the larval or prepupal period.

2. Diapausing prepupae usually contain a higher proportion of dry matter than do normal individuals.

3. Diapause occurs because the corpus allatum (Weismann's ring) is not producing the necessary hormone.

4. Diapause is ended when prepupae are removed from sand to empty tubes. Probably the corpus allatum is stimulated by a nervous reaction; the reaction is not due to an increase in the rate of metabolism.

5. Low temperatures (5° C.) do not affect the hormone, but high ones (35–37° C.) destroy it.

6. Prepupae of Lucilia sericata have salivary glands which are dilated to nearly a quarter the body size. The contents serve as a store of water during diapause.

7. Diapausing prepupae after desiccation drink water and return to their original body weight. The water increases the volume of blood in circulation, and the blood controls the size of the adult produced.

8. Diapause in nature enables the species to survive unfavourable conditions.