THE 
VOYAGE OF H.M.S. CHALLENGER. 
ZOOLOGY. 
REPORT on the Entozoa collected by H.M.S. Challenger during the Years 
1873-76. By Dr. 0. von Linsto w of Gottingen. 
XwjL 
'/ 
INTRODUCTION. 
The number of Entozoa included in the spoils of the Challenger Expedition is remark- 
ably small in comparison with the large collection of Vertebrates. This is mainly due to 
the fact that the exploration was for the most part marine, and not terrestrial, and that 
it concerned not only the regions near the coast, but also to a very large extent the deep 
sea. For it follows from the nature of the life-history of Helminths, that these forms 
must occur more and more sparsely in proportion to the distance from the shore. In the 
Nematoda, Gordiacea, Acanthocephala, Trematoda, and Cestoda, with few exceptions 
(among Nematodes and Trematodes), the sexually mature forms are parasitic in some 
organ, such as the stomach, which communicates with the outer world, and from 
which the numerous eggs pass out with the excrement. On the soil or in the water the 
ova find their way into another organism, within which they develop into larvae, and are 
usually encapsuled until they pass along with their intermediate host into the original 
victim, where they become sexually mature. Not a few Helminths, such as many 
digenetic Trematodes and the Gordiaceae, have in their developmental cycle to pass 
through two intermediate hosts. That the Vertebrata which inhabit the high seas are 
remarkably free from Helminths is without doubt due to the fact that the ova are too 
widely scattered in the infinite mass of water to have much chance of reaching their 
proper intermediate hosts ; and, further, that even when they do so, there is again in the 
(ZOOL. CHALL. EXP. PART LXXI. — 1888.) Bbbb 1 
I 
