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HANDBOOK OF INVERTEBRATE ZOOLOGY. 



of the egg shown in Fig. 191, after it has been thus treated. 

 The centre of the germinal area is occupied by a number 

 of small spherules which are irregularly spherical, and 

 each of which contains a very large nucleus. 



As we pass from the centre of the cap towards the pe- 

 riphery, the spherules become larger, and at its growing 

 edge they are replaced by large flattened pyramids (6, b), 

 which radiate out on all sides, upon the surface of the 

 yolk (a), and gradually pass into the surface of the yolk, 

 without any distinct boundary at their outer ends. 



Fig. 192. — More highly magnified view 

 of the growing edge of the blastoderm of the 

 egg shown in Fig. 191, after staining with 

 osmic acid and borate of carmine. (Drawn 

 from nature by W. K. Brooks. ) 



a. Unsegmented yolk. b. Segmentation 



' i^yramids. c. First row of cells, which have 



been formed by separation from the ends of 



the pyramids, d. Second set of cells, which 



have been formed by the division of cells 



similar to d. d". Fourth set, similar to d 



Careful examination shows that the segmentation spher- 

 ules are pretty regularly arranged with reference to these 

 pyramids. Just inside the broad inner ends of the pyra- 

 mids, there is a ring of large spherules (c), equal in num- 

 ber to the pyramids, and presenting every indication of 

 having l)een just formed by the separation of the proximal 

 end of each pyramid from the larger distal portion. In- 

 side these there is a second ring of spherules [d'), about 

 half as large, and exactly twice as numerous as the first 

 set, and so placed that a pair of the spherules of the 

 second set are pretty nearly in a straight line with one of 

 the first set and the base of a pyramid. Each pair of this 



