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INEZ WHIPPLE WILDER. 



granules, although among these cells there have already appeared 

 well-developed mucous cells which are filled with their secretion 

 and are already discharging it into the lumen. The duodenum 

 leads rather abruptly into the right anterior region of the cylin- 

 drical yolk mass, beneath the posterior margin of the liver. 



In this mass of yolk cells two types of cell may be distinguished, 

 a smaller and a larger (ys and yl, Fig. n). The smaller ones lie 

 peripherally, have a spherical or slightly columnar form with a 

 well-defined nucleus usually in the peripheral end of the cell. 



c 



FIG. 10. Cross sections at the same level through the middle of the body of 

 (c) a 13 mm. embryo; (b) newly hatched larva, terrestrial stage A (cf. Fig. 12, a. 

 and Plate I., Figs, i and 2;; (c) larva 3 days old, terrestrial stage] C (cf. Fig. 12, c, 

 and Plate I., Figs. 5 and 6); (d) larva 15^ days old, terrestrial stage F (cf. Fig. 12, d, 

 and Plate I., Fig. 9). Note the gradual reduction of the mass of yolk cells (y) and 

 the formation of the intestinal lumen (lm); ms, mesonephros. Enclosure between 

 the dotted lines in (a) indicates the location of Fig. n. Drawn with Abbe camera. 

 X 



The cell walls are definite, the contained yolk granules~of varying 

 size, but among them relatively few large ones. The remaining 

 portion of the yolk mass consists of enormous cells which are 

 often multinucleate, with very large, irregular nuclei. The cell 

 walls are not always clearly defined and in many regions seem 



