From the researches of Onchi and Nishio it is known that the encysted larva of Heterophyes nocens Onchi et Nishio is found in the Japanese mullet. H. nocens is closely allied to H. heterophyes v. Siebold, which is found commonly in. man, dog and cat in Egypt. It may be assumed that the larva of the Egyptian Heterophyes will be found likewise in certain fishes allied to the mullet. On the homeward voyage from my tour in Europe I examined some specimens of mullet in Port Said, for the purpose of finding the young larva in them, and was fortunate enough to discover encysted larva. I carried back with me some of these fishes fixed by formalin. After returning to Chosen (Korea) I examined the parasite, and found that it certainly belongs to a species of Heterophyes. Its morphological description is given in the present short communication.

Since Looss described in detail the anatomy and histology of the type species of the family Ancylostomida no attempt has been made to study comparatively any of the other genera of this group.

From its economic importance as a little-known, though frequent, parasite of ruminants and its scientific importance as type species of the second sub-family of the AncylostomidcB, Monodontus trigonocephalus has been selected for description.

(1) The female can and does lay eggs.

(2) The eggs in the body of living worms do not develop beyond the 16-celled stage.

(3) The eggs passed in the fæces of chickens are in the same stage of development as those in the uteri of the adult.

(4) The eggs take about a week to develop and produce infective larva?, when cultured in well aerated water at a. temperature of about 25°C.

(5) The embryos undergo only one moult before reaching the infective stage.

(6) The second stage or infective larvae are generally ensheathed. They are non-climbers, do not penetrate the skin, and cannot resist dessication.

(7) In the body of the host the larvae soon reach the lungs, where they grow considerably in size and undergo two further moults.

(8) The final or fourth stage larvae are reached in about five days after infection.

(9) The larvae then copulate and migrate into the trachea where they attain sexual maturity in from 10 to 14 days later.

(10) The whole life cycle is completed within a month.

Japanese observers have found the encysted cercarire of Heterophyesnocens in the Japanese mullet which belongs to the genus Mugil. In Egypt, Heterophyes heterophyes is a fairly common parasite of man, dog and cat. The genus Mugil “Egyptian mullet” is represented in Egypt by three species.