350 



OILMAN A. DREW. 



into the unoccupied space dorsal to the stomach. The cells 

 are no longer arranged to form definite walls (figs. 36 — 39, z.)j 

 but later some of them seem to form liver pouches again 

 (figs. 42 — 44) . A small portion of the space into which the 

 stomach and liver are crowded is not filled, and finally forms 

 the pericardium (figs. 39 — 41). 



The rupture of the liver pouches leaves the dorsal part 

 of the stomach without side walls, and the dorsal wall is 

 commonly broken (figs. 37 and 39). The dorsal wall is formed 

 again before the liver pouches regain their cavities (fig. 40). 

 Some of the separated liver cells find their ways into the 

 open stomach (figs. 37 and 38), and together with mucus 

 practically fill it. For a period of two or three days after 

 casting, the animal is not active, and it is doubtful if it 

 feeds. At the end of this time the walls of the stomach 

 begin to re-form, and the mass of material that has filled the 

 stomach has largely disappeared. For a number of days 

 the liver does not form definite pouches. The rounded and 

 scattered cells are finally collected into two masses (figs. 40 

 and 42) that finally form new liver lobes. The left is slightly 

 larger than the right mass, but the masses are more nearly 

 equal in size than is the case with Yoldia. In both cases it 

 seems that the difference in the size of the two liver lobes 

 causes the developing loops of the intestine to take up a posi- 

 tion on the right side. Cavities gradually extend out into the 

 liver pouches from the stomach (figs. 43 and 44). In the 

 formation of the cavities some of the rounded cells seem to 

 go to pieces in much the same way as they would if digested. 



The elongation of the intestine that results in the forma- 

 tion of the loops begins about the time that the embryo 

 acquires its fourth pair of gill plates (fig. 45). This elonga- 

 tion carries the portion of the intestine that lies dorsal to the 

 posterior adductor muscle toward the posterior wall of the 

 stomach and nearer the dorsal margin of the shell. The end 

 of the loop is forced over to the right side, and is extended 

 anteriorly nearly to the anterior wall of the stomach. At 

 this stage (Text-fig. 0) the loop of the intestine is much like 



