224 



O. C. GLASER. 



Here too Osborn found hiatuses, but if these really occurred in 

 the living state, it is difficult to see how a sac with holes in both 

 its inner and outer linings could contain the eggs which these 

 larvae ingest. 



When the fully gorged cannibals transform into veligers, the 

 changes undergone by the entoderm are as striking as those in 

 the external form of the larvae. These changes lead to regional 

 differentiation, the outcome of which is that the dorsal cells of the 

 digestive tract come to be very unlike the ventral ones, whereas 

 between these two zones, laterally, there are transitional cell 

 forms. In addition to this morphological differentiation which 

 holds true of the digestive tract from its most anterior end back 

 to the region where it becomes identical with the digestive gland 



or liver, there is a well- 

 marked physiological dif- 

 ferentiation between the cells 

 in the oesophageal region 

 and those posterior to this 

 zone. Fig. 4 shows a sec- 

 tion, based on the study of 

 several, through the oeso- 

 phagus. The lumen of the 

 tube is lined by compara- 

 tively small cells, provided 

 either with several nuclei, 

 or with lobed ones. ■ The 

 cytoplasmic contents of 

 these cells are quite granu- 

 lar, and are often so 

 densely crowded along the 

 inner surfaces of the cell membranes that the nuclei in these cases 

 seem to float in clear lakes of non-tingible cell sap. 



The outer border of the oesophagus has a very different ap- 

 pearance. The cells there in many cases show unmistakable 

 signs of disintegration, especially ventrally v, where often cell- 

 fragments and quite isolated nuclei can be seen. Dorsally d 

 the outermost cells are very large, polynuclear, frequently without 

 complete cell-membranes, and their contents which are granular, 



Fig. 4. A transverse section through the 

 oesophageal entoderm of a larva in stage IV., 

 based on the study of several sections through 

 this region. Z, left ; r, right ; v, ventral ; 

 d, dorsal. 



