TAENIOGLOSSA. 401 



The main peculiarity of the body consists in the large size of the head 

 and foot, and the small size of the visceral sac. The foot is divided into an 

 anterior part the so-called pro- and mesopodium (Fig. 315 p) and a posterior 

 part the metapodium. The former is foliaceous, and often carries a sucker on 

 its posterior part ; while the latter, considerably elongated and extended far 

 backwards, forms the caudal continuation of the body. 



The visceral sac is either spirally twisted and enclosed by a mantle and spiral 

 shell (Atlanta), or has the form of a projecting mass, which is placed over the 

 hinder part of the foot, and is likewise covered by the mantle and a reduced 

 hat-shaped shell (Carinaria) ; or finally, the visceral sac is reduced to a small, 

 scarcely-projecting nucleus, which is covered on the front side by a membrane 

 with a metallic lustre, and is completely without a shell. 



The nervous system is well-developed. The cerebral ganglia are conjoined, 

 and the pleural are fused with them (visibly in Atlanta and Pterotrachea). 

 There are two pedal connectives on each side, which are partially free proximally 

 in Atlanta. The pedal ganglia are situated at the base of the fin (pro-meso- 

 podium). The visceral commissure is long, streptoneurous, and provided with 

 several ganglia, but without dialyneury or zygoneury (p. 365). In the Carinariidae 

 there are secondary viscero-pedal anastomoses which are not twisted. In the 

 Firolidae the pedal connectives are fused with the anterior part of the visceral 

 commissure ; and behind the pedal ganglion the two branches of the visceral 

 commissure are fused together for the greater part of their extent. 



The osphradium has the form of a more or less elongated ciliated organ in 

 the pallial cavity to the left of the ctenidium. The otocysts are close to 

 the cerebral ganglia. The eyes are very large, contained in capsules, and 

 moved by special muscles ; they are highly elaborate and are placed at the 

 base of the tentacles, which are entirely absent in Pterotrachea. 



The alimentary canal has a protractile pharynx with radula, a long oeso- 

 phagus slightly swollen towards its middle, and a stomach and liver placed 

 behind. The intestine is short and is not curved forward in Pterotrachea. 



The heart is near the stomach ; it is in front of the gill in Pterotrachea, but 

 is disposed as in the Platypoda in the less specialized forms. The arteries 

 terminate abruptly in the blood-sinuses. The ctenidium is monopectinate, not 

 covered by mantle-fold in Pterotrachea, and absent in Firoloida. The kidney 

 is a transparent sac with contractile walls ; it has the same relations as in 

 other Gastropods, and opens not far from the anus. 



The males are distinguished by the possession of a large penis, which projects 

 freely on the right side of the foot. The males of Pterotrachea possess a sucker 

 on the hinder part of the anterior division of the foot ; in Atlanta and Carinaria 

 the sucker is present in both sexes. The ovaries and testes fill the posterior 

 part of the visceral sac, and are partially embedded in the liver. The ducts 

 open on the right side of the body near the anus. There is a ciliated groove 

 to conduct the sperm from the generative opening to the penis. The penis 

 is provided with a glandular appendage or flagellum. The oviduct possesses 

 a large albumen gland and a receptaculum seminis opening into it. 



The Heteropoda are exclusively pelagic animals, and are often found in great 

 numbers in the warmer seas. Their tissues and shell are transparent. They 

 are somewhat clumsy in their movements, which are effected with the ventral 

 surface uppermost, by oscillations of the whole body and fin. They are all 

 carnivorous. When the tongue is protruded, the lateral teeth fly apart from 

 one another like the limbs of a pair of forceps, and when retracted they again 



2 D 



