304 J- Beard 



parthenogenesis as a disguised hermaphroditism, in which each egg 

 produces the equivalent of a Spermatozoon for itself (in the seeond 

 polar body) and in which self-impregnation oceurs. 



BovERi, Hertwig and others have in recent years thrown a flood 

 of new light over this matter in their investigations into the egg- and 

 sperm-formation in the Nematoda. 



In this connection the Myzostomidaì form an interesting group 

 for investigation ; for in them, as in some other hermaphrodites, of 

 two apparently similar cells, lying side by side, one may become 

 an egg-cell, while the other may give rise to spermatozoa. 



BovERi and Hertwig have shown that there is no essential 

 morphological difl'erence between the egg-mother-cell and the sperm- 

 mother-cell, and thus, indiiectly, they have helped to consolidate 

 the vievv that hermaphroditism may arise as a secondary condition, 

 in what were primarily dioecious forms. And theoretical difficulties 

 in the way of the conclusion, that the hermaphroditism of Myzostoma 

 may be a secondary state, are thus largely relieved. If the herma- 

 phroditism w^ere primitive in this case, two things would be difficult 

 of explanation. The first of these would be the actual existence of 

 true males, and the seeond their small size as compared with the 

 hermaphrodites. 



It is impossible to conceive that any natural cause should lead 

 to the evolution of dwarf-raales from hermaphrodites. An evolution 

 of this sort would be meaningless in such cases as the Cirripedia, 

 Artemia^ or the Rotatoria, where it would ultimately end in a form 

 nnfitted for the struggle for existence, or even incapable of preforming 

 sexual fuuctions. 



It is significant to note the comparative frequency of the asso- 

 ciation of dwarf-males and hermaphrodites, and of the occurrence of 

 degeneration in such males. And, while it is rare — even impossible 

 in the animai kingdom — to find males, hermaphrodites and fé males 

 within the limits of a single species, the co-existence of true males, 

 usually dwarfed, with hermaphrodites is not at ali infrequent. With 

 the doubtful exception of the Trematoda i parthenogenesis and herma- 

 phrodidsm would appear never to obtain together within the limits 

 of a single species. The one would apparently exclude the other; 



1 The recent work of W. R. Coe (Z. Jahrb. Abth. Morpli. 9. Bd. p. 561) 

 does not teod to verify the existenee of parthenogenesis here. 



