GASTROPODS. 



363 



exclusively holostomatous, that is, with uninterrupted apertures. Gastropteron, 



which typifies another family, is remarkable for the great lateral expansions, or 



epipodia, which are used by the animal in swimming, The gill lies exposed on 



the right side, the head-shield is truncate in front and pointed behind, and the 



mantle terminates behind in a slender, whip-like appendage. At one time this 



mollusc was supposed to be shell-less, but in reality an internal shell does exist ; 



but, as it is only ^ - of an inch in diameter, it may be easily overlooked. G. 



meckeli, of the Mediterranean, is of a vivid red colour, with 



a few white spots, and a pale or bluish border to the lobes. 



In the Philinidce, as typified by Philine, the shell is very 



thin, and wholly concealed beneath the mantle. In form 



it somewhat resembles Bulla, but has the aperture larger. 



P. aperta, a very common British species, lives in shallow 



water all round the coast, feeding upon foraminifera and 



even small sea-urchins. The animal is white, has a very 



large frontal-shield, but no tentacles or eyes. It is provided, 



as in the case of Scaphander, with a powerful gizzard. The ova, which are very 



numerous, are deposited in a single series, in a long and loosely -twisted cord, 



enclosed within an ovoid, gelatinous capsule. 



The sea-hares (Aplysiidai), so called on account of a slight resemblance to a 

 crouching hare, and not for their nimbleness of foot, are elongate creatures, with 

 a long neck, distinct head, oral and dorsal tentacles, and furnished beneath the 

 mantle with a shelly plate to protect the branchiae. The mouth is provided with 



Philine aperta (nat. size). 



sea-hare, Aplysia (nat. size). 



horny jaws, and the gizzard is armed with horny spines, which prepare the food 

 for digestion. The sides have large thin lobes, which are either folded over the 

 back, or used in swimming. Aplysia includes both animal- and vegetable-feeders, 

 inhabiting shallow water in all parts of the world. In olden time there were 

 many stories in vogue respecting the poisonous nature of the sea-hare, but it has 

 been shown to. be harmless. It has the faculty of emitting a nauseous smell ; and 

 a beautiful purple fluid is discharged from glands in the edge and inner surface 

 of the mantle. The species illustrated (A. depilans) occurs on the coasts of France 



