HYMENOPTERA 



317 



producing male broods. The history of cleavage as well as of the embry- 

 onic cells is the same in fertilized and unfertilized eggs. 



The freshly deposited egg is a pear-shaped cell, surrounded by a thin 

 but tough membrane (Fig. 265) and averaging 0.155 mm. in length. The 

 nucleus {nu) is near its anterior end. In fertilization the sperm enters the 



nu.p 



Fig. 268. Fig. 269. 



Fig. 265. — Litomastix. Fertilized egg. {os) Oosome. {nu) Nucleus, (sp) Sperm. 



Fig. 266. — Litomastix. Fertilized egg after second maturation division. (^1) Outer 

 nucleus of first polar body. (A2) Inner nucleus of first polar body. (51) Second polar body 

 nucleus. (B2) Female pronucleus, {os) Oosome. (sp) Sperm. 



Fig. 267. — Litomastix. (Al) Outer nucleus of first polar body. (52) Female pronucleus. 

 {nu. p) Polar nucleus ( = A2 + 51). {os) Oosome. {sp) Sperm. 



Fig. 268. — Litomastix. With two cleavage nuclei. {Al) and (J.2) First polar bodies. 

 (51) Second polar body, {nu) Cleavage nuclei, (os) 05some. 



Fig. 269. — Litomastix. Two-cell stage. (Al) First polar body nucleus, {nu. p) Polar 

 nucleus, {nu) Cleavage nucleus, {os) Oosome. 



egg at any point on the surface of the posterior region. Polyspermy 

 never occurs. Within the egg is the oosome ("germ-line determinant"), 

 a nucleolus-like body (os). Maturation is identical in fertihzed and 

 unfertilized eggs. The first maturation division results in reducing the 

 number of chromosomes from sixteen to eight. The second division, but 

 without reduction, follows immediately upon the first or may even precede 

 it (Fig. 2QQA1,A2,B1). The result of these two divisions is the formation 

 of three polar bodies (A1,A2,B1) and the ootid (B2), the latter forming 

 the female pronucleus. 



