162 



THE GASTROPODA 



heart. In the Atlantidae there is an aortic bulb ; the arterial vessels 

 always end abruptly in sinuses. The ctenidium is inonopectinate and 

 completely enclosed in the pallial cavity in Atlanta (Fig. 141, i), but it pro- 

 jects in Carinaria (Fig. 142, i\ is no longer covered by the mantle in Ptero- 

 trachea (Fig. 143, In-}, and finally has completely disappeared in Firoloida. 

 The kidney is a transparent and sometimes contractile sac, which has the 

 same relations as in other Taenioglossa and opens not far from the anus (Fig. 

 141, 7). The gonad is situated beside the liver (Fig. 141, ?c). The genital 

 duct is always rather short, and opens alongside of the anus ; in the male 

 it exhibits a dilatation, the vesicula seminalis (Figs. 141 and 142, y), and its 

 aperture communicates with the penis by means of a seminal groove. The 

 penis is situated at the base of the foot, and is provided with a glandular 



FIG. 142. 



I'arinaria wcditerraneii, male, right-side view. A, the animal ; Ji, the shell removed ; C, /), 

 two views of the shell of ilimiiopotltt. a, mouth and odoiitophora ; b, cephalic tentacles ; c, eye ; 

 </, the tin-like anterior lobe of the foot ; d\ its sucker ; , posterior part of the foot ; /, salivary 

 glands ; h, margin of -the mantle ; i, ctenidium ; ?, oesophagus ; n, stomach ; o, anus ; j>, liver ; 

 t, aorta, springing from the ventricle ; n, cerebro-pleural ganglion ; r, pedal ganglion ; w, testis ; 

 x, visceral ganglion ; y, vesicula seminalis ; z, penis. (From Lankester, alter Souleyet.) 



appendage or flagellum. In the female the genital duct is furnished 

 with a copulatory bursa and an albuminiparous gland. The Heteropoda 

 lay floating eggs imbedded in a gelatinous matrix ; the larvae are charac- 

 terised by the velum, which is divided into four or six lobes. All the 

 Heteropoda are pelagic and transparent, and are generally found in dense 

 bands in warm and temperate zones, swimming slowly in a reversed 

 position, that is to say, with the foot uppermost. They are all car- 

 nivorous. The tribe includes three families which afford a good example 

 of regressive evolution accompanying a process of detorsion and a return 

 to bilateral symmetry, as in the Opisthobranchs. The specialisation of 

 the group is marked by a progressive reduction, and finally by the 

 disappearance first of the operculum, afterwards of the mantle, and 

 finally of the ctenidium and tentacles. The genus Atlanta is still 

 provided with a well-developed coiled shell and an operculum, and is 



