HERMAPHRODITISM. 



71 



individuals on a branch, while genuine hermaphroditism of individual 

 polyps also occurs. Among hydrozoa (zoophytes, swimming-bells, jelly- 

 fish), hermaphroditism is a rare exception, or, we may almost say, rever- 

 sion. The common hydra, which is a somewhat degenerate type, is 

 hermaphrodite, though at the same time individuals may be found with 

 only ovary or only testes. EleutJieria is also hermaphrodite, and " abor- 

 tive ova occur in the male of Gonothyrea loveni.'^'' Sometimes a colony is 

 hermaphrodite {Dicoryne)^ but the stems and individuals unisexual. Some- 

 times a stem is hermaphrodite, but the individuals unisexual (certain 

 sertularians). Among jelly-fishes the genus Chrysaora is known to be 

 hermaphrodite. 



(3.) " Worms.'''' — The condition of the sexual 

 organs varies enormously among the diverse 

 types lumped together under the title of 

 "worms" or "Vermes." In the lowly tur- 

 bellarians, all the genera are hermaphrodite 

 except two, but, as in many other cases, the 

 organs do not reach maturity at the same time, 

 the male preceding. In the related trematodes 

 or flukes, hermaphroditism again obtains, with 

 one exception, or perhaps two. The certain 

 exception is the curious parasite Bilharzia, 

 where the male carries the female about with 

 him in a " gynaecophoric canal," formed of 

 folds of skin. In the adjacent class of cestodes 

 or tapeworms, all the members are hermaphr 

 rodite. These three classes are doubtless re- 

 lated, but it seems plausible to connect the 

 retention of hermaphroditism with the de- 

 generacy of parasitism, and also with the rich, 

 yet at the same time stimulating nutrition, 

 which may favour the retention of double 

 sexuality. The utility of the hermaphrodite 

 state, if the eggs of these animals are to be 

 fertilised and the species maintained, can 

 hardly be doubted, but this does not explain 

 the facts. It is important to notice too, that 

 self-fertilisation — that is, union of the eggs and 

 sperms of the same organism — has been proved 

 to occur in several trematodes, and seems to 

 be almost universal in cestodes. This may be one of the conditions of the 

 degeneracy of these parasites, for frequent as hermaphroditism is among 

 plants and animals, self-fertilisation is extremely rare. 



Hermaphroditism is rare among the free-living nemerteans, but con- 

 stant in the semi-parasitic leeches. The only exception to separateness of 

 the sexes among threadworms or nematodes is the very curious case of the 

 genus Aiigiostoimim. Here, in an organism which is anatomically a female, 

 the reproductive organ starts with producing spermatozoa, which fertilise 

 the subsequent ova. The animal is thus physiologically hermaphrodite, 

 and at the same time self-impregnating. Approaching the higher annelid 

 worms, we find the primitive Protodrilus hermaphrodite ; the earthworms 

 are constantly so, but all their marine relatives have the sexes separate. 



iiilharzia, a parasitic trematode, 

 in which the male carries the 

 female in a special fold of skin 

 called the " g^maecophoric 

 canal." — After Leuckart. 



