424 



PTEROPODA. 



blished by zoologists, and some important modifications have 

 been detected in their organization ; although, in all of them, the 

 lateral alee form the instruments of progression. 



The Clio borealis, anatomized by Cuvier,* and more recently 

 and completely investigated by Professor Eschricht of Copen- 

 hagen,'!' is one of the species best known, as well as most abun- 

 dantly met with ; it is, therefore, by a description of this Ptero- 

 pod that we shall proceed to introduce the reader to the general 

 facts connected with the history of the animals under consideration. 



The body of the Clio is about an inch in length, of an oblong 

 shape, and terminating posteriorly in a point ; while at the oppo- 

 site extremity there is a little head supported upon a short neck, 

 and furnished with delicate retractile tentacles, apparently instru- 

 ments of touch. The locomotive organs, as the name of the class 

 imports, consist of two delicate wing-like appendages (Jtg> 198, 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 appara- 

 tus exactly comparable to the double-paddled oar with which the 

 Greenlander so dexterously steers his kajac, or canoe, through the 

 very seas inhabited by the little Clio we are describing. 



(466.) The head of one of these animals is surmounted by va- 



Fig. 198. 



A B C 



* Memoire sur le Clio borealis. 



f- Anatomische Untersuchungen iiber die Clione Borealis, von D. F. Eschricht. 

 Kopenhagen, 1838, 4to. 



