518 A. M. CABK SAUNDKKS AND MAKGAHET I'OOLE. 



of the two large irregular spaces generally to be seen in the 

 two endomeres. '^Iliese coalesce and form a cavity within 

 the liver, which communicates with the stomach by an 

 irregular gap in the wall of the latter on the right side and 

 rather ventrally. Text-fig. 20 is a section taken through 

 this gap. On the left side is seen the cavity of the stomach 

 communicating with the cavity of the liver; on the right 

 side is the right liver, to be described later on. The 

 nuclei have divided and are reduced in size. The size and 

 shape of the liver in the free-swimming larva can be made 

 out from PI. 22, figs. 8 and 9. It may roughly be considered 

 to consist of two lobes, of which the left is derived from B and 

 the right from A. The left lobe is much the largest; it covers 

 the left wall of the stomach, projects anteriorly to it, and 

 rises dorsally. The right lobe lies ventrally, projecting 

 beyond the stomach on the right side. The liver is clothed 

 externally by a fine epithelium of flattened cells. During 

 the whole of the embryonic period the yolk is being con- 

 sumed, and when the larva emerges from its capsule it is 

 entirely used up. The liver now takes on a new function^ 

 presumably one of secretion and digestion, for we have often 

 observed algae and other food material in the cavity, and 

 drops of secretion are at times to be seen in the cells. 



The right liver is formed in an entirelv different manner. 

 At a time between the stages represented in PL 22, figs. 4 

 and 5, certain cells of the right anterior wall of the stomach, 

 rather nearer the dorsal than the ventral surface, become 

 pushed out to form a flat, knob-like process (i?. L). This 

 gradually takes on a rounder shape, and the contained cavity 

 increases in size, while it becomes constricted off from the 

 stomach to form a definite organ, which is the right liver. 

 In the free-swimming larva it is nearly round, and com- 

 municates with the stomach only by a small and somewhat 

 iri'egular aperture. When fully formed it lies almost entirely 

 dorsal to the stomach, the smaller retractor muscle passes 

 above it and the intestine below and to the right. The cells 

 composing it are of large size, the cytoplasm consisting of a 



