MOLLUSCA. 



165 



A remarkable circumstance regarding the reproduction of 

 some genera, is stated on tiie autiiority of Chamisso. The 

 SalpcE iFiij. 155) arc found linked together in long chains; 



Fig. 155.— BipnoR*, one oi- the Salpj..* 



after a time their union is dissolved, and each individual pro- 

 pagates a solitary young one. This attains the full size of 

 the species, and then brings forth a social chain o& young 

 salpce, which again give origin to solitary individuals; — "so 

 that a salpa mother," to use Chamisso's familiar expression, 

 "is not like its daughter or its own mother, but resembles its 

 grand-daughter and its gi-andmothor.'"t 



BRACHICPODA. 



These are bivalve Mollnsca, and, like some of those just 

 mentioned, are destitute of the power of locomotion. They 

 are attached to foreign bodies, and are furnished with two 

 long ciliated arms {Fig. 156; hence the name of the class, 

 " arm-footed." They are found abundantly in a fossil state. 

 The species now existing are kv,- in number, and some of them 

 have been brought up from depths of from sixty to ninety 

 fathoms. jMr. Owen, in reference to this circumstance, re- 

 marks, that both the respiration and nutrition of animals 



• Fig. 155. — a. Mouth. ^ Liver, &c. — 4, Branchial Sac. — m. Muscular Bands. 

 — A, Heart.— n, Nen-ous Ganglion. 



t Stecnstrup on AltematioD of Generations, page 39 



