HERMAPHRODITISM 5 



sac living in a Holothurian (Synapta digit ata), which possesses none 

 of the characteristics of either the gastropods or any molluscs, and in 

 the interior of which there is nothing to be observed but the organs 

 of generation and the embryos. Nevertheless, the Entoconcha is 

 decidedly a parasitic snail, as is clearly proved by its larvae, but 

 it is a snail which, in consequence of parasitism, has lost all the 

 characteristics of molluscs in its mature condition, but still exhibits 

 them in the early stages of development. 



Certain nematodes show very clearly to what devious courses 

 parasitism may lead. The Atractonema gibbosum, the life-history of 

 which has been described by R. Leuckart, and which lives in the 

 larvae and pupae of a dipterous insect (Cecidomyia), exhibits, in its 

 early stage, the ordinary characteristics of other threadworms. A 

 few weeks later the males having died off immediately after copu- 

 lation the females are transformed into spindle-shaped bodies, the 

 mouth and anus of which are closed. They carry with them an irregu- 

 larly shaped appendage, in which the segmenting ova are situated 

 and in which the further conditions of life of the Atractonema are 

 accomplished. A minute examination has demonstrated that this 

 appendage is the prolapsed and enlarged vagina of the creature which 

 has become merely a supplementary attachment. The conditions 

 present in the Sphaerularia, the nematoid nature of which was long 

 undiscovered, are still more remarkable. It was only when Siebold 

 proved that typical nematodes were hatched from their eggs 

 that their nature was recognised. The nematodes thus produced 

 have not the slightest resemblance to the parent. 



The researches of Lubbock, A. Schneider, and more particularly 

 of R. Leuckart, have shown that what we call Sphaerularia bombiis not 

 an animal but merely an organ the vagina of a nematode worm. 

 This vagina at first grows, sac-like, from the body of the tiny nema- 

 tode ; it gradually assumes enormous dimensions, (2 cm. in length) ; 

 it contains the sexual organs and parts of the intestine ; the remain- 

 ing portion of the actual creature then becomes small and shrivelled ; 

 it may be easily overlooked, being but an appendage to the vagina 

 with its independent existence, and it finally disappears altogether. 



The GREAT FERTILITY of parasites is another of their peculiarities, 

 though this may be also the case to a certain degree with some of 

 the free-living animals, the progeny of which are likewise exposed 

 to enormous destruction. 



More remarkable, however, is the fact that the young of the 

 endoparasites only very exceptionally grow to maturity by the side 

 of their parents ; for they always sooner or later leave the organ 



