296 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



immediately migrates back into the yolk of the egg without giving off a 

 second polar body. Immediately after the polar body has separated from 





) 



pb- 



> V i 



FiQ. 236. — Brachyrhinus. Nucleus {nu) and polar body (pb) 15 minutes after egg laying. 



the pronucleus, the chromosomes appear distinct enough to indicate that 

 there is no reduction in number. In several cases about 25 chromosomes 



(,,, — -u in both the nucleus and the polar body 



: :^,,^.(*- N have been counted. Later counts mad{^ 



/ ••. in cleavage nuclei migrating into the 

 'v-_^-'^ periphery during blastoderm formation 

 , j- confirm this number as being equal to 



T ) the somatic number of chromosomes, 

 1^ : indicating that parthenogenesis in this 



(yf^ I be(>tle is the diploid type. 



\jy\ 'X About the time the nucleus is again 



^P** _^,y near the center of the egg, the polar 



:* ) body divides, and one of the resultant 

 — ;'' nuclei is pushed out under the vitelline 



membrane and entirely cut off from the 

 ,J- cytoplasm (Fig. 237). In the meantime 



::0/ • ■ the first cleavage division has taken 



. ..;t*(ii^§!if:^:y-f.:-::; place, and the daughter nuclei are 



Fig. 237.— Brachyrhinus. Polar body, migrating toward the periphery. Be- 

 tween the ninth and the twelfth hours there are 16 to 32 in the yolk. At 

 18 hours the daughter nuclei have increased in number and have reached 



