. The Biological bulletin. Biology; Zoology; Marine biology. 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 o
. The Biological bulletin. Biology; Zoology; Marine biology. 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. â 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, ven
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