554 PTEROPODA. 



furnished with delicate retractile tentacles, apparently instruments of 

 touch. The locomotive organs, as the name of the class imports, con- 

 sist of two delicate wing-like appendages (fig. 277, a a) attached to the 

 two sides of the neck, by means of which, as by a pair of broad fins, 

 the Pteropod rows itself about with facility. But the two aliform 

 membranes, although externally they appear separate instruments, are, 

 as we are assured by the observations of Professor Eschricht, but one 

 organ, being made up entirely of muscular fasciculi, which pass right 

 through the neck and spread out on each side in the substance of the 

 wing, forming an apparatus exactly comparable to the double-barrelled 

 oar with which the Greenlander so dexterously steers his kajac, or 

 canoe, through the very seas inhabited by the little Clio we are de- 

 scribing. 



(1482.) The head of one of these animals is surmounted by various 

 organs appropriated to different offices, and some of them not a little 

 remarkable from the amazing complication of structure which they 

 exhibit. On each side of the oral opening are three conical appendages 

 (fig. 277, c, s), that to a superficial examiner might appear to be mere 

 fleshy tentacula ; but in reality they are instruments of prehension, of 

 unparalleled beauty and astonishing construction. Each of these six 

 appendages, when examined attentively, is seen to be of a reddish tint ; 

 and this colour, under the microscope, is found to be dependent upon 

 the presence of numerous minute isolated red points distributed over 

 its surface. When still further magnified, these detached points are 

 evidently distinct organs, placed with great regularity, so as to give a 

 speckled appearance to the whole of the conical appendage ; and their 

 number, at a rough guess, may be estimated at about three thousand. 

 Every one of these minute specks is, in fact, when more closely ex- 

 amined, a transparent cylinder, resembling the cell of a polyp, and 

 containing within its cavity about twenty pedunculated disks, which 

 may be protruded from the orifice of their sheath (fig. 278, c), and 

 form so many prehensile suckers adapted to seize and hold minute prey. 

 Thus, therefore, there will be 3000 x 20 x 6=360,000 of these micro- 

 scopic suckers upon the head of one Clio an apparatus for prehension 

 perhaps unparalleled in the creation. 



(1483.) When not in use, the appendages referred to are withdrawn, 

 and concealed by two hood-like fleshy expansions, which, meeting each 

 other in the mesial line, completely cover and protect the whole of this 

 delicate mechanism, as represented in (fig. 277, A). 



(1484.) Still, however, even when the hoods are drawn over the 

 parts they are intended to defend, the Clio is not left without tactile 

 organs wherewith to examine external objects ; for each valve of the 

 hood is perforated near its centre : and through the apertures so formed, 

 two slender filiform tentacula (fig. 277, c, fc), somewhat resembling the 

 feelers of a Snail, are protruded at the will of the animal ; and by 



