GERM CELLS OF HERMAPHRODITES 193 



Proterogyny has been described in certain ascidians 

 (Salpa), pulmonate gasteropods, and corals. That 

 hermaphrodites are not sexless but really animals 

 with double sex is well shown by the life history of 

 a worm, Myzostoma pulminar, which passes through 

 a short male stage during which spermatozoa are 

 produced, then a stage when no functional germ cells 

 are formed, and finally a female stage, characterized 

 by the development of eggs (Wheeler, 1896). Thus, 

 in this species, although hermaphroditic, there is no 

 functional hermaphroditic stage. All variations be- 

 tween this entire separation of the periods of germ- 

 cell development and the simultaneous production 

 of male and female germ cells have been recorded. 

 Some degree of protandry has been observed among 

 the sponges, ccelenterates, flatworms, segmented 

 round-worms, mollusks, echinoderms, Crustacea, and 

 chordates. 



Hermaphroditism may occur in only a few families, 

 genera, or species in a class. This is true, for example, 

 among the anthropods and vertebrates. Normally 

 the insects are called dioecious, but among bees, ants, 

 and butterflies, and more rarely other groups, individ- 

 uals appear which exhibit male characters on one side 

 of the body and female characters on the other, or the 

 anterior part may be male, the posterior female, etc. 

 (von Siebolt, 1864 ; Schultze, 1903 ; Morgan, 1907, 

 1913). Such a phenomenon is known as gynan- 

 dromorphism. Several hypotheses have been pro- 

 posed to account for this condition. Boveri has 

 suggested that if the egg nucleus should chance to 



