68 EDWARD DRANE CRABB. 



elusions. The earliest observations on the manner of reproduction 

 in hermaphroditic gastropods available are those of Aristotle who 

 states that the individuals of the group of Testacea (which in- 

 cluded Gastropoda) reproduce like plants, the inference being that 

 they spring from the mud or water. Strange as it may seem, ac- 

 cording to Baudelot ('63) no one appears to have questioned 

 Aristotle's views until about the end of the sixteenth century when 

 an Italian naturalist, Aldrovandi, stated that copulation occurs 

 among the snails. Although Wagner ('35, p. 304) had already 

 indicated the fact that* both sperms and eggs are derived from a 

 single gonad and pass through a common duct before reaching the 

 male and female conduits, most of the descriptions of the re- 

 productive system of hermaphroditic gastropods published before 

 the latter half of the nineteenth century fail to recognize the true 

 nature of the ovotestis. Even Cuvier ('46) states that Lyninaa 

 and Planorbis have the ovary and testis separate. 



Among the most recent investigations of parthenogenesis in 

 Gastropoda may be mentioned the work of Pelseneer ('19) on 

 three species of Lymncra and that of Robson ('23, '26) on 

 Paludestrina jcnkinsi. Pelseneer claims that eggs from his iso- 

 lated snails gave off only one polar body. Colton ('18) found that 

 the eggs of isolated Lymncea columella regularly give off two polar 

 bodies. 



The most important cytological work on reproduction in pond 

 snails is that of Colton ('18) in which he states that he found 

 ripe sperms and ova in a single acinus in the ovotestis of Lymnaa 

 columella. Diver ('25) deplores the lack of cytological investi- 

 gation of the problem. Since neither the presence of two polar 

 bodies in these eggs nor the fact that ripe sperms and ova occur 

 in a single acinus at the same time does not preclude the possibility 

 of parthenogenesis, these investigators have not solved the prob- 

 lem of reproduction in hermaphroditic snails. 



In most cases the conclusions appear to be based upon scant 

 evidence. For instance, only one case (Baltzer, '13) has been 

 found in which the results obtained by isolation or breeding ex- 

 periments have been substantiated by further cytological evidence 

 than has already been mentioned. Although an enormous amount 

 of classical embryological work has been done on gastropods, be- 



