HERMAPHRODITISM. 77 



pigmy males, often several, leading a shabby existence as parasites, (4.) 

 In other species of Scalpelhim and Ibla the same pigmy males occur, but 

 attached, as we have noted, to hermaphrodites, which in these forms have 

 replaced the true females. (5.) Lastly, in many genera, like Follkipes, 

 only hermaphrodites occur. 



What Darwin did for the cirripedes, Graff has done for another very 

 curious set of animals, the Myzostomata. These are degenerate chcetopods 

 or bristle-footed v/orms, which occur as outside parasites on sea-lilies 

 (crinoids), on the arms of which they make curious galls. The majority 

 are hermaphrodite, but again some species have the sexes separate, and 

 again in a few cases complemental males have been demonstrated. If the 

 hermaphrodite condition was here primitive, it persists in the majority of 

 cases ; thus, IMyzostonia glabriirn is hermaphrodite, with a minute com- 

 plemental male ; AI. cysticoliim has the sexes distinct, but the female is just 

 emerging from (or approaching) hermaphroditism, for it includes rudi- 

 mentary testes ; in M. tenuispinuni, injlator, murrayii, there are separate 

 sexes, with the females predominating in size. One conclusion, at least, 

 is vividly suggested by these curious facts, the tendency of the male form 

 to become reduced to a vanishing point. 



§ 9. Conditions of Hertnaphroditism. — In looking back over 

 the cases where normal hermaphroditism occurs, a few general 

 conclusions are readily drawn. Thus Claus points out that 

 hermaphroditism finds most abundant expression in sluggish 

 and fixed animals. Flat-worms, leeches, earthworms, tardi- 

 grades, land snails, &c., well illustrate the first of these ; and 

 among sponges, sea-anemones, corals, polyzoa, bivalves, &c., we 

 find frequent illustration of the association of fixedness and 

 hermaphroditism. Most of the tunicates are also fixed, and all 

 are hermaphrodite. Claus notes further, how in flukes and 

 tapeworms hermaphroditism is associated with isolated habit of 

 life. The isolation, however, is only sometimes true, for flukes 

 may occur near one another in great numbers ; and as many as 

 ninety tapeworms {Bothriocephalus) have been known to occur 

 at one time in a single host. 



Simon has gone further, in insisting on the real connection 

 between quiescent and parasitic habit and the hermaphrodite 

 condition. In flukes and tapeworms, leeches, Myzostomata, 

 and some cirripedes, we find the association of hermaphroditism 

 with a more or less intimate parasitic habit. It will be remem- 

 bered, too, that the hagfish, in which hermaphroditism is 

 common, is also to a large extent a parasite. But what Simon 

 points out is, that organisms on which great demands are made, 

 especially in the way of muscular exertion, cannot afford to be 

 hermaphrodite ; while a plethora of nutrition, as in parasitism, 

 tends to make the persistence of the double state possible. He 

 gives numerous illustrations of this very reasonable contention. 



