Goi-m-Cells ill Clirvsoiiiolid Hoetles. 259 



Here the first cleavage divisions take place. A number of the earliest 

 cleavage stages were found (2, 4, 6, 16, etc.) in all of which the 

 majority of the nuclei were nearer the anterior than the posterior 

 pole. This anterior position of the early cleavage nuclei has already 

 been described- for Coleoptera in Hydrophilus (Ileidei', 1889), and 

 in many insects belonging to other orders. 



As cleavage progresses a separation of the nuclei into two sections 

 takes place. The nuclei of one group form a more or less regular 

 layer equidistant from the periphery at all points except the posterior 

 end ; here a space wider than elsewhere separates them from the 

 surface of the egg. This layer is composed of preblastodermic nuclei 

 (by nucleus is meant the nucleus plus its accompanying cytoplasm) 

 which move outward, fuse with the "Keimhautblastem" and produce 

 the blastoderm. The nuclei of the other group (vitellophags) remain 

 behind scattered throughout the yolk. 



When the preblastodermic nuclei have almost reached the periph- 

 eral layer of cytoplasm (Fig. 5) it is possible to distinguish those 

 whose descendants will come in contact with the pole-disc from the 

 neighboring nuclei which will produce ordinary blastoderm-cells. 

 This distinction can be made more easily in a polar surface view 

 (Fig. 12) which shows the entire pole-disc. Such a view discloses 

 eight nuclei lying directly under the central area of dark granules. 

 These nuclei, as we shall show later, divide twice before reaching the 

 periphery of the egg. Some of the nuclei thus produced will, how- 

 ever, pass outside the margin of the disc and take part in blastoderm 

 formation; the others, which will enter this granular area and become 

 the pole-cells, can be traced back to the row of four nuclei which lie 

 in the center of the pole-disc nearest the surface of the egg. At this 

 stage (Fig. 5) all of the nuclei within the egg are similar, the various 

 stains used (see the chapter on methods) failing to bring out any 

 differences in structure. Differentiation takes place only when those 

 nuclei in the posterior region fuse with tlie "Keimhautblastem." 

 Continued division brings the preblastoderm-nuclei into the position 

 shown in Fig. 0, where they again increase in number by mitosis. 

 In the section figured (Fig. 0) all of the nuclei are in the prophases 

 of mitosis, and each of those nearest the pole-disc (Fig. G, a) has its 



