No. 644] ARRESTED EVOLUTION 



263 



hermaphroditism is still a matter of dispute (see Geddes 

 and Thompson, pp. 83, 84) for while some, as Simon, 

 attribute it to a plethora of nutrition (as especially in 

 parasites), others are " content to interpret it as an adap- 

 tation to ensure fertilization, for the possibilities of pair- 

 ing between separate sexes are certainly lessened if the 

 animals are sluggish, sedentary or parasitic." There is 

 likewise difference of opinion as to whether the stage 

 of hermaphroditism is the lower, and the condition of 

 distinct sexes has been derived from it (G-egenbaur), 

 or whether it is a secondary condition, derived from 

 primitive uni-sexuality as claimed by Pelseneer who con- 

 siders it grafted on the female sex in MoUusca, Crustacea 

 and Pisces (Greddes and Thompson, p. 8-t). 



Considering its prevalence among the lowest classes 

 with sexual reproduction, notably the sponges and corals, 

 and again among the Cirripedia, we believe that herma- 

 phroditism is in the former an inherited primitive char- 

 acter and in the latter an acquired one. At any rate, 

 since it is so frequently and distinctly associated with 

 sessility, as in the just mentioned Cirripedia, and in 

 many pelecypods (oyster) and with sluggishness in other 

 pelecypods and many gastropods, and since it is exactly 

 these same groups which contain numerous persistent 

 types, it seems probable that hermaphroditism is a fur- 

 ther reproductive condition contributor}- to persistence. 



(d) Reproduction hy Parthenogenesis. — Parthenogene- 

 sis is the mode of propagation in at least one typically 

 persistent genus, viz., Apus; but it has also become a 

 confirmed physiological habit in other archaic t}T)es of 

 crustaceans among the branchiopods, as notably in Ar- 

 temia, the brine-shrimp, in Branchipus, and in Limna- 

 dia; further in the equally primitive water-fleas {Daphnia 

 and Moina) and finally, among the ancient ostracods, 

 also in some species of the common Cypris. 



Of the whole class of Branchiopoda, which through 

 paleontology, and notably through the recent amazing 



