13^ whitman: [Vol.1. 



when the formation of free nuclei begins. Near the upper 

 angle of xy, between xy and a, is seen a well-defined entoderm 

 cell. It is rare to find the entoplasts assuming the cell form 

 at such a depth. Fig. 5 (a horizontal section in the plane 

 of the arrow 5-5, Fig. 3) shows entoplasts at different depths, 

 one of which has become defined as a cell {en), while another 

 near by shows faint indications of its future outline. 



Passing now to the stage in which the germ-bands have 

 united for about one-half their length, we find all the entoplasts 

 in the periphery of the yolk, and a marked advancement 

 already made in the development of the cephalic end. Beneath 

 the stoniodaeal thickening (Fig. 20, PI. VI.) is seen a mass of 

 large clear cells (^«), as yet presenting no definite form and 

 giving no indication of their future histological character. 

 They are easily identified with the entoderm cells beneath the 

 cephalic lobe in Figs. 3 and 4. 



In a little later stage (Fig. 21, e?t), v/hen the germ-bands are 

 nearly closed, these cells are smaller, and appear to be taking 

 a more definite shape, as they become more sharply delimited 

 from mesodermic (wz) and neural {sup, oe, g) elements. We 

 now distinguish an anterior axial portion, forming a solid pad 

 beneath the stomodeeum, and a posterior portion {sgl), con- 

 sisting of larger cells, stretching towards the dorsal and ventral 

 sides. Those of the dorsal side are more deeply stained than 

 those of the ventral side. In several instances I have seen a 

 column of these clear cells extending through the centre of the 

 stomodaeum, as shown in Fig. 21 ; and this leads me to 

 believe that the canal of the proboscis is' lined throughout 

 with cells of entodermal origin. The condition shown in Fig. 

 22) fully bears out such a view. Along the ventral side of the 

 yolk (Fig. 22) there is a peripheral layer of coarsely granular 

 protoplasm ( " conche protoplasmique granuleuse " of Nus- 

 baum), feebly stained, in which may be seen free nuclei {cup). 

 Similar nuclei are found on the dorsal side, but there they are 

 less numerous, and the peripheral layer of granular, uncolored 

 protoplasm is not present. 



By the time the germ-bands are completely closed, and the 

 embryo is ready to leave the egg membrane (Fig. 28), the 

 entoderm of the oesophageal region has differentiated into small, 

 axially placed cells, of a distinctly epithelial character, and 



