298 



LOWER INVERTEBRATES. 



Leaving theSe curious parasites, which, so far as known, ai-e unrepresented on our 

 shores, we come to forms which undoubtedly belong to the Nudibranchiata, and which 

 lead free lives in the seas of all parts of the globe. 



Passing by the Phyllidid^e, a small family of tropical and semi-tropical forms, in 

 which the gills are either absent or enclosed between the mantles and the foot, we 

 come to the Eltsiid^e, in which the body is shaped much like a common garden slug, 



Fig. 336. — Pontolimax capitans. 



the gills have disappeared, and the tentacles are simple or absent. This family is 

 represented in our figures by Pontolimax capitans, a form only a tliird of an inch in 

 length, found on the coasts of northern Europe. It lives between tides, feeding on 

 minute algae, and lays its eggs in small, pear-shaped capsules, each containing on the 

 average about one hundred eggs. Pontolimax sonata occurs on the New England 

 coast. In Elysia, the typical genus of the family, the tentacles are well developed 

 and the sides of the body are expanded into a pair of wings, which stop just behind the 

 neck. Elysia viridis of the Eurojiean seas is of a green color, as is also our New England 

 E. chlorotica, and the closely allied Ehjddla catullus. These forms are not uncom- 

 mon, creeping about on the eel grass (Zostera) of our northern coasts. 



Fig. 337. — Eiytiia viridis. 



In the EoLiD^, a much larger family than the last, the gills, which may be 

 lammated, papillose, or like plumes, are arranged along the sides of the back, while the 

 tentacles are capable of being reti-acted into sheaths. The genus Teryipes, which is 

 represented by a little species common upon the stems of hydroids, received its name 

 from old Forskal, from a belief that it walked upon its back, using its gills as locomo- 

 tory organs. The branchiaj are eight in number, arranged in a single row of four on 



