62 AKT. 4. X. YATSU : 



The wall of the oesophagus, it should here be noted, comes 

 in the dorsal-most portion, in close relation with the integument of 

 the neck. The latter, a thin epithelium, is here actually apposed 

 to, and wraps around, the thick columnar cells of the oesophagus 

 (PI. VIL, Figs. 91, 93, 95). 



Near, but not quite at, the end of the oesophagus is a 

 valve-like elevation of the wall, which reduces the calibre of the 

 canal. This indicates the boundary between the parts formed of 

 the ectoblast (=the stomodœum.) and entoblast (PI. V., Figs. 77, 

 79, and PI. VIL, Fig. 93). In living larvae cilia appear to be 

 planted differently, as they point away from one another, (PL V., 

 Fig. 80), those that are anterior to the boundary being directed 

 anteriorly, and those posterior to it posteriorly. The current is, 

 however, the same in both parts, being toward the liver. In 

 section the difference between these two parts is striking : the 

 nuclei of the anterior part are longer than those of the posterior 

 part and, moreover, the direction of the nuclei of these two parts 

 is different, inclining away from the boundary (PI. VIL, Figs. 

 93, 105). 



The liver is derived from the main part of the stomach 1 and 

 is the chief seat of digestion. This part I shall refer to as the 

 liver, although its function is obviously not equivalent to that of 

 the vertebrate organ of the same name. The walls of the liver 

 consist of a thick glandular epithelium (PL VIL, Figs. 93, 94, 

 103, 104) whose cytoplasm is highly glandular and whose nuclei 

 are spherical, closely applied to the base of the cells. In this 



1. Hitherto I have used the term "stomach" in quite a different sense from the same 

 term employed in the adult anatomy. I have used the term for the spacious sac posterior 

 to the oesophagus. This "stomach" has now differentiated into the liver and the mid-gut, 

 and the "stomach" as such has, therefore, vanished. Still 1 shall call the central cavity 

 the stomacal cavity. The adult stomach is formed de novo (vide infra). 



