214 KELLIID/E. 



extremities, not observed before, being the only ones 

 that remained to perform their functions externally. 

 These produced a partial current without propelling the 

 animal through the water, as at this stage it gave up its 

 natatory habits and took to a quiet life. The internal 

 portion, the parts of which could not be very distinctly 

 made out, appeared to be undergoing a process of deve- 

 lopment. The mass was continually changing its form, 

 the separate parts being extended alternately in different 

 directions, and a portion, probably the incipient foot, 

 was occasionally pushed beyond the margin of the shell. 

 At this point of development further observations were 

 unfortunately arrested by the death of the whole colony 

 in consequence of the water becoming impure, and my 

 situation at a distance from the sea preventing my get- 

 ting an immediate fresh supply. The whole period that 

 I had kept them was not above five or six clays ; so that 

 their development had been pretty rapid. After the 

 death of the animals the shells remained at the bottom 

 of the glass. They were of an elliptical form, straight 

 at the upper margin, where they were attached, though 

 the hinge did not appear to be yet formed ; the whole, 

 excepting in the elongated form, had very little resem- 

 blance to the adult shell." 



I am sure my readers will not regret my having 

 reproduced such a faithful and striking picture by one of 

 our great masters of British zoology. It agrees on the 

 whole with the account furnished by Loven, and espe- 

 cially with his observations as to the development of 

 the embryo of Modiolaria marmorata and Lasaa rubra. 

 The metamorphosis in Modiolaria is stated to have 

 commenced about the third day after the spawn was 

 deposited, being the same period as that which Alder 

 noticed in Mont acuta ferruginosa. The shell is apt to 



