HERMAPHRODITISM. 73 



we have noted, to hermaphrodites, which in these forms have replaced 

 the true females. (5) Lastly, in many genera, like Pollicipes, only 

 hermaphrodites occur. 



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

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

 chaetopods or bristle-footed worms, 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, Myzostoma glabrum 

 is hermaphrodite, with a minute complemental male; M. cysticolum has 

 the sexes distinct, but the female is just emerging from (or approach- 

 ing) hermaphroditism, foj it includes rudimentary testes; in M. tenuis- 

 pinum, inflator, 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. 



IX. Conditions of Hermaphroditism. — In looking back over 

 the cases where normal hermaphroditism occurs, a few general conclu- 

 sions are readily drawn. Thus Claus points out that hermaphrodit- 

 ism finds most abundant expression in sluggish and fixed animals. 

 Flatworms, leeches, earthworms, tardigrades, land-snails, &c. , well 

 illustrate the first of these; and among sponges, sea-anemones, corals, 

 polvzoa, bivalves, &c. , we find frequent illustration of the associa- 

 tion 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 

 habits 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 (Bothriocephahis) 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 inti- 

 mate parasitic habit. It will be remembered, 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, can 

 not afford to be hermaphrodite; while a plethora of nutrition, as in 

 parasitism, tends to make the persistence of the double state pos- 

 sible. He gives numerous illustrations of this very reasonable con- 



