I48 THE PINEAL ORGAN 



The existence of the same types of shell — or parts of the shell, such as 

 the operculum — in the living and fossil representatives of a species 

 indicates a persistence of type which has gone on through countless ages, 



R.Ft. 



Li. ... ! Str.Ad. 



^ i J Sm Ac 



An. 



Ext.r.ap 



G.cf 



Fig. 106. — Drawing of a Scallop (Pecten), showing the Position of Pallial 

 Eyes. (After Pelseneer.) 

 An. : anal aperture. 

 Ext. r. ap. : external renal aperture. 

 Ft. : foot. 



G.$, G.$ / male and female parts of gonad. 

 Ht. : heart. 

 Li. : liver. 

 P. : palp. 



Pal. eyes : pallial eyes. 

 R. Ft. : right foot. 

 Sm. Ad. : smooth adductor muscle. 

 Str. Ad. : striated adductor muscle. 

 St. : stomach. 

 V.g. : visceral ganglion. 



and also allows of the inference being made that the primary sense- 

 organs, such as the paired ocelli and statocysts of the veliger larvae of the 

 living animals, were present also in the larva; of the corresponding 

 fossil representatives of these species. Further, it is from these simpler 



