162 THE GASTROPODA 
heart. In the Atlantidae there is an aortic bulb; the arterial vessels 
always end abruptly in sinuses. The ctenidium is monopectinate and 
completely enclosed in the pallial cavity in Atlanta (Fig. 141, 2), but it pro- 
jects in Carinaria (Fig. 142, 7), is no longer covered by the mantle in Ptero- 
trachea (Fig. 143, br), and finally has completely disappeared in F%roloida. 
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, q). The gonad is situated beside the liver (Fig. 141, w). 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 ofa seminal groove. The 
penis is situated at the base of the foot, and is provided with a glandular 
Fia. 142. 
Carinaria mediterranea, male, right-side view. A, the animal; B, the shell removed; C, D, 
two views of the shell of Cardiopoda. a, mouth and odontophore ; 0, cephalic tentacles ; ¢, eye ; 
d, the fin-like anterior lobe of the foot ; ’, its sucker ; e, posterior part of the foot; f, salivary 
glands ; h, margin of the mantle ; 7, ctenidium ; m, oesophagus ; 7, stomach ; 0, anus; p, liver ; 
t, aorta, springing from the ventricle ; w, cerebro-pleural ganglion ; ¥, pedal ganglion ; w, testis ; 
2, visceral ganglion ; y, vesicula seminalis ; z, penis. (From Lankester, after 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 
