386 PROCEEDINGS OF THE ACADEMY OF [April, 
regions. As development proceeds it is elongated, its posterior end 
being ventrally directed and turned toward the right. The develop- 
ment of the liver of Crepidula comes later, being retarded by the 
great amount of yolk. 
The next change in the development of the enteron of Fiona may 
be observed in fig. 105, which represents a veliger in which the ali- 
mentary canal is beginning to become differentiated into several parts, 
Anteriorly is seen the stomodzeum, which has as yet not broken through 
but touches the wall of the enteron. Above and to the left of this. 
point of contact is a decided lobing of the wall of the enteric cavity, 
formed of the large yolk-ladened cells which at an earlier period lay in 
the anterior region of the archenteron. This is the rudiment of the 
liver,and as development proceeds the invagination becomes larger and 
more constricted at its base, forming a rounded lobe upon the left dorsal 
wall of the enteric canal. Behind the rudiment of the liver the enteron 
has widened into a capacious sac which is larger at its upper anterior 
end, the walls of the whole being formed of rather small cells which are 
yet rich in yolk. This is the stomach, and it ends blindly against the 
intestinal mass behind and to the right. The intestine is yet a solid 
strand of cells connecting the posterior end of the stomach with the 
ectoderm. With the growth of the veliger this strand has become 
more slender, elongated and turned forward, its distal end lying well 
up on the side of the body behind the constriction which forms the 
foot. The huge excretory cell lies just dorsal to this point (figs. 106, 
107). In figs. 90, 91, 92 and 93, which represent coronal sections of 
a veliger somewhat older than figs. 105 and 106, and slightly more 
mature than that of fig. 107, it will be seen that the intestine is still a 
solid strand of cells, and that the cesophagus is as yet not in open con- 
nection with the rest of the alimentary canal. An examination of a 
considerably older larva (figs. 109, 110) shows a very small lumen, 
just beginning to form in the center of the intestinal strand, but as 
yet no communication between cesophagus and enteric cavity. 
Stomodeum and Mouth. 
As the blastopore narrows (fig. 79) it becomes entirely surrounded, 
except at the anterior end, by third quartet cells. At the anterior 
point second quartet cells from 2b” and 2b’ lie along the edge also. 
Figures of a later stage (as 97, 98) show the blastopore as a mere 
rounded opening, its edges and walls below thickly set with darkly 
nucleated cells, and when complete closure occurs a plug of these cells 
