Cximings — Morphogenesis of Platy atrophia. 



19 



stands nearer the radical stock than any other. The case in 

 which the nepionic ventral fold remains simple and unmodified 

 throughout the life of the individual certainly must be con- 

 sidered as more primitive than the case in which the nepionic 

 fold bifurcates. It is known that in nepionic and early 

 neanic stages of brachiopods, plications are added by implanta- 



Fig. 7. Platystrophia lynx from Vevay, Indiana, snowing variation in num- 

 ber of plications of fold and sinus, ajt'", ventral, anterior, posterior and pro- 

 file views of a normal individual with the normal number, three in sinus and 

 four on fold ; bb', ventral and anterior views of individual with four pli- 

 cations in sinus, the fourth originating by bifurcation of the left lateral ; 

 cc', ventral and anterior views of individual with five plications in sinus, the 

 two additional plications are implanted, c", diagram showing method of 

 origin of plications ; ee' , individual with six plications in sinus ; del" (with 

 diagrams to left of cl' and d"), individual with seven plications in sinus; 

 d', dorsal ; d" , ventral views. Author's collection. 



tion except in highly accelerated types. We must believe, 

 therefore, that a tendency of the primary plication of the 



