51, 



Figures 50 and 51 represent longitudinal sections of a 

 gill, taken in tlie pla^ies indicated in figure 36. Tlie cliitfnous 

 bar is cut in one, but tlie plane of the other lies below it. 

 These sections shov/ the gill to be rather evenly ciliated. Later 

 stages, after the lobes have elongated, show the cilia to be con- 

 fined to t}ie side next to the mantle. The third lobe is formed 

 from the ventral lobe, which broadens and then constricts in the 

 manner detailed above. Other lobes are foimied in a similar man- 

 ner. 



The alimentary canal elongates, bends ventral ly, and 

 the stomach enlarges. In from two to four days after the test 

 is cast, tiie liver poviches reappear. At first they do not jiave 

 very definite walls, but they gradually become well defined, and 

 it is noticeable that the large scattered cells disappear at a 

 corresponding time. The two po'aches are no longer symmetrical, 

 the left being prolonged posteriorly, fills up the space between 

 the dorsal end of the stomach and the intestine, figures 36 and 

 66. The greater development of the left liver lobe at this early 

 date, ver^'- likely affects the futiore position of the intestine, 

 a loop of A-^^ich comes to lie on the right side of the animal, very 

 near the shell. 



Abovit the 25th day, a ridge, corresponding in position 



