542 PROCEEDINGS OF THE ACADEMY OF [DeC., 



and soon a large group of cells is found in this region (cf. fig. 36). A 

 careful study of the eggs themselves leaves no doubt but that they all 

 arise from the primitive entoblasts. PI. XXXIX, fig. 33, shows the 

 spindles for the first division of these cells. I have repeatedly found 

 eggs showing the second and later divisions of these cells, but in every 

 case it has been found impossible to make an intelligible drawing of the 

 egg. The fact that these eggs cannot be rotated under the cover glass 

 has added greatly to the labor of finding eggs suitable for study or 

 drawing. In this case it has effectually blocked all attempts to por- 

 tray a certain stage. The material itself, however, leaves no doubt 

 that the divisions take place as described. I have attempted to 

 embody the essential facts of these divisions in the schematic text 

 fig- 2. 



During all this time the very large nuclei of the three anterior cells 

 of the fourth quartet, 4a, 4b and 4c, can still be found (fig. 34). Pre- 

 vious to this time there has been some shifting of the relative positions 

 of the fourth cjuartet cells. At the time the mesentoblast cell is budded 

 into the interior (fig. 19) all the foiu- cells of this quartet lie in nearly 

 the same plane. The two lateral cells, 4a and 4c, are perhaps slightly 

 higher than the others. When 4d^ divides bilaterally these two cells 

 overlap 4a and 4c. With the further development of the mesento- 

 blast on the interior of the egg and the ectoblast on the outside, the 

 large cell 46 is pressed upwards. A narrow process from this cell runs 

 along the centre of the egg, and in this, reaching almost from one side 

 of the process to the other, lies the enormous nucleus of 46 (figs. 32 and 

 34). The nuclei of 4a and 4c are also pressed up along the sides, but 

 not so high as that of 46. These three cells are closely crowded 

 together, and while their boundaries remain distinct for some time 

 (fig. 32) they tend to become obliterated. 



In the meantime an interesting process has been going on within 

 these cells. As has been noted by all previous students, the yolk 

 granules tend to fuse together, thus forming homogeneous fat-like 

 drops. As Selenka and Lang have noted, this breaking up of the yolk 

 is not accompanied by nuclear division. The process is more or less 

 irregular, but one or two regular features can usually be recognized. 

 The first one of these spherules to be formed is from the anterior and 

 ventral portion of the cell 46. At first the centre of these spheres is 

 composed of granules, while around its periphery the granules dissolve 

 into a fluid substance. Soon j^fterwards smaller spheres appear in this 

 cell and in 4a and 4c. No nuclear division is concerned in this process, 

 for the undivided large nuclei of all three of these cells can be followed 



