156 



GASTROPODA. 



(Fig. 67), which, however, are considerably shorter than those just 

 mentioned. In Carina r/'a, again, the streamers are longer, and the 

 lobes, cut up into three parts, cause this larva greatly to resemble 

 that of Firoloida (Gegenbauk and Krohn). 



The great development of the locomotory organs in the Heteropoda 

 causes their metamorphosis to be very marked. At its commence- 

 ment, a cylindrical process with a rounded free end appears on the 

 anterior side of the foot immediately in front of its base (Figs. 66 and 

 67, fl) ', this soon lengthens and carries on continuous swinging 

 movements. This is the rudiment of the fin which, in its origin, must 

 be regarded as belonging to the foot. In the course of metamor- 

 phosis, the cylindrical process becomes flattened laterally, and thus 



77Z-. 



Fig. 68.- Lateral aspect of a Oarinaria (after Souleyet and Gegenbaur). a, anus ; 

 abfj, abdominal ganglion: at, auricle; "", eye; bg, buccal ganglion; bm, buccal 

 mass ; eg, cerebral ganglion ; d, intestine ; /, tentacles ; ,//, fin ; k, gill ; /, liver ; m , 

 mouth; ///", stomach; n, kidney;^, pedal ganglion; s, sucker; sc, shell; sj>, 

 salivary gland ; sw, tail ; vd, oesophagus : re, ventricle. 



approaches the form of the keel-like fin of the adult (Fig. 68, fi). 

 This flattening extends from behind forward ; for a time, in the already 

 keel-shaped fin, a portion of the former cylindrical process is found ; 

 this, in Firoloida, is attached somewhat nearer the anterior margin, 

 but in Pterolrw.kea somewhat further back. By degrees this also is 

 drawn into the flattened fin (Krohn). In some species of Atlanta, 

 the fin appears from the first as a laterally flattened projection on the 

 anterior side of the foot and thus here more nearly resembles its 

 definitive shape. In this form, also, the sucker can already be seen, 

 lying close to the posterior margin of the keel-like foot, this position 



