D.—ZOOLOGY. 121 
in Japan and other parts of the world. These worms when mature live 
in pairs, a male and female, in the veins of the lower part of the 
abdomen, especially in the wall of the bladder and of the rectum. The 
eggs, laid in large numbers by the female worm, provoke inflammatory 
changes, and cause rupture of the veins of the organs invaded. Until 
about ten years ago the life-history of Schistosoma had been traced 
only as far as the hatching of the ciliated larva or miracidium which 
takes place shortly after the egg reaches water, but it was then shown 
that this larva is not, as had been held by Looss, the stage which infects 
man. Miyairi and Suzuki (1913) found that the miracidium of Schisto- 
soma japonicum entered a fresh-water snail which acted as the inter- 
mediate host, and Leiper and Atkinson (1915) confirmed and extended 
this observation, and showed that the miracidia develop into sporocysts 
in which cercarie are formed. We owe chiefly to Leiper’s work (1915- 
1916) our knowledge of the life-history and method of entry into man 
of the Egyptian species of Schistosoma. He demonstrated that two 
species of this parasite occur in Egypt, and established that the miracidia 
develop in different intermediate hosts: those of S. mansoni enter 
Planorbis, while those of S. hematobium penetrate into Bullinus—the 
molluscs being abundant in the irrigation canals. The sporocysts 
produce cercariz, which escape from the snails and gather near the 
surface of the water, and experiments with young mice and rats showed 
that the cercarie attach themselves to the skin, enter, and reach the 
portal system from which they travel to the veins of the lower part 
of the abdomen. Infection of man takes place chiefly through the skin 
when bathing or washing in water containing the cercariez, though infec- 
tion may also occur through drinking such water. And so, at last, 
these worms which have troubled Egypt for at least thirty centuries 
have become known in all their stages, and measures for preventing 
infection—which were of great use during the War—have been devised, 
and curative treatment introduced. 
Other recent helminthological researches deserve consideration did 
time permit, for there has been much excellent work on the life-history 
of the liver-flukes and lung-flukes of man, and the life-cycle of the 
tape-worm, Dibothriocephalus latus, was worked out in 1916-17. 
Mention should also be made of Stewart’s investigations (1916-19) on 
the life-history of the large round-worm Ascaris lumbricoides, during 
which he made the important discovery that the larve on hatching in 
the intestine penetrate into the wall and are carried in the blood to the 
liver, and thence through the heart to the lungs, where they escape from 
the blood-vessels, causing injury to the lungs. The larve, now about 
ten times their original size, migrate by way of the trachea and pharynx 
to the intestine, where they grow to maturity. During last year Dr. 
and Mrs. Connal have worked out the life-history of Filaria (Loa) loa 
in two species of the Tabanid fly, Chrysops, and investigations on other 
Filarias have thrown light on their structure, but there is still need for 
further researches on the conditions governing the remarkable periodi- 
city exhibited by the larve of some species (e.g. F. bancrofti; in some 
parts of the world the larve of this species are, however, non-periodic). 
The period under review has obviously been one of great activity in 
