MOLLUSCA. 



165 



A remarkable circumstance regarding the reproduction of 

 some genera, is stated on the authority of Chamisso. The 

 (Fig. 155) are found linked together in long chains; 



m b h 



Fig. 155. BIPIIORA, ONE OF TIIK SAI.I-.I:.* 



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 of* young 

 salpn*., 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 grandmother."! 



BKACHIOPODA. 



THESE are bivalve Mollusca, 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 few in number, and some of them 

 have been brought up from depths of from sixty to ninety 

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

 marks, that both the respiration and nutrition of animals 



* Fig. 155. or, Mouth. -f, Liver, &c. b, Branchial Sac. m, Muscular Bands. 

 A, Heart. n, Nervous Ganglion. 



f Steenstrnp on Alternation of Generations, page 39 



