NAKED-GILLED SUBGROUP 3329 



These are inclosed in a perfectly transparent mucus, and the fry generally emerges 

 in about ten days or a fortnight. L,ike Scyll&a, the animals known as Glaucus live 

 in the open sea upon floating seaweed, and feed upon jellyfish of various kinds. The 

 form of the body is peculiar, having three lobes or expansions on each side, sup- 

 porting the linear branchiae. Pelagic animals generally seem to be either colorless 

 or specially colored, with a view to protection from enemies both above and below 

 the surface of the water. Probably the blue color of lanthina is protective, as re- 

 sembling that of the ocean water. The blue tint of Glaucus may also serve this 

 purpose. 



This group of Nudibranchs comprises a number of forms which 

 a have no external branchiae, but effect respiration through the general 

 ciliated surface of the body. A typical example of this section is illustrated by the 

 figure of Elysia viridis (p. 3328) which is a little creature about an inch in 

 length, of a dark green color, varied with white, greenish-blue, and reddish-white 

 dots. It lives upon seaweed, and, owing to its color, is difficult of observation. 

 The absence of external branchiae is noticeable, and the ramified blood vessels seen 

 in the lateral expansions of the body are presumed to be connected with the respira- 

 tory function. This is the only species found upon the shores of Britain, and is 

 most common on the south and southwest coasts. It is said to mimic the color of 

 the different seaweeds upon which it occurs. Limapontia is another example of the 

 Pellibranchs. It is slug-like in form, but without any tentacles. The species 

 figured (L. capitata) is a minute animal, about a sixth of an inch in length, chiefly 

 of a black color, but occasionally somewhat transparent and colorless. Alder writes 

 that " this curious little animal is probably pretty generally diffused, but on account 

 of its minute size it ma} r readily be overlooked. It is gregarious; and, wherever 

 met with, it has usually been found in abundance, appearing when contracted like 

 little black dots scattered over the conferva on which it feeds." It lives between 



Limapontia capitata (much magnified.) 



tide marks, feeding upon small algae, and deposits its ova in small pear-shaped 

 capsules, each containing about one hundred eggs. 



The only form belonging to this group, the position of which is not 

 settled, is the parasitic genus Entoconcha. The animal is worm-like 

 and spirally coiled, and attaches itself by the oral end (#) to one of the blood ves- 

 sels (E), within the visceral cavity of a certain group of Echinoderms. One species 

 is found in Synapta, and a second (E. muelleri] occurs in the trepang (Holothuria) 

 of the China Sea. In the very early or larval state Entoconcha is contained in a 

 minute operculated glassy shell. The subsequent changes between this and the 

 209 



