242 PTEROPODA. PART in. 



our own coasts. When put into sea- water it expands till 

 it is about an inch long (fig. 175). It is then pellucid, 

 tinged with pink, and the central tubes in its numerous 

 papillse are of a rich crimson hue, their surface reflects 

 a metallic blue, and their tips are opaque white ; as the 

 animal keeps its papillse in constant motion the effect 

 is very pretty. 



The Eolis coronata, like all its congeners, has a 

 stinging apparatus, consisting of an oblong bag, full of 

 thread cells, placed at the extremity of each papilla, 

 from whence darts can be ejected through an aperture 

 in the tip. The whole of the Eolididse are carnivorous, 

 fierce, and voracious, setting up their papillse like the 

 quills of a porcupine when they seize their prey ; they 

 tear off the papillse of their weaker brethren, and even 

 devour their own spawn, though their chief food con- 

 sists of zoophytes. 



The Pteropoda, or wing-footed mollusca, are very 

 small ; they are incapable of crawling or fixing them- 

 selves to solid objects, but they are furnished with 

 two fins like the wings of a butterfly, with which they 

 float or row themselves about in the ocean, far from 

 land in vast multitudes. The shell of the typical spe- 

 cies Hyaleea (A, fig. 177), which resembles the thinnest 

 transparent glass, consists of two valves, one, which is 

 placed on the front of the animal, is long, flat, and ends 

 in three points ; the other valve, which is applied to the 

 back, is short and convex, and in the lateral fissure be- 

 tween the two, the mantle is protruded. The head and 

 fins project from an opening at the top of the shell. 

 The fins, which are formed of muscular fibre, are fixed 

 on a short thick neck, with the mouth lying between 

 them, containing a tongue crossed by rows of long re- 

 versed teeth. The head has no tentacles, and the 

 animal appears to be blind, but it has an auditory 

 vesicle lined with cilia, which keeps a few otolites in 



