eg BIOLOGICAL LECTURES. 



the second polar globule. At this time (Fig. 13) the sixteen 

 chromosomes that are to remain in the &gg are closely packed 

 together near the animal pole, and are almost in contact with 

 the inner sphere of the aster. The inner sphere is derived from 

 the centrosome of the first maturation-spindle (see No. 8) and 

 r:^^ has the following structure : it is a 



1^ spherical body with a perfectly defi- 



---o ',-/Q^')-1<5^.>v nite wall, containing a non-staining 



'•°J'^^f''^$^^-^)0''CC^f^^'- substance in which is excentrically 

 " v^i Xi>i ° V"" ° placed a single centrosome united 



^STls\if^^. ° to the wall by a few strands. The 



cK^'"vJ---f-ci(K> cytoplasm in the immediate vicinity 



VV"T~Off is arranged in the form of an aster, 



the fibres of which are centrally 

 attached to the inner sphere ; the 



Fig. 14. — Unio. Small portion of the . it 



upper pole. Egg-nucleus reconslitut- firSt I'OW Of miCrOSOmCS OU thC radl- 



ing ; 



sphere-substance forming. atious of thc astcr bouttd a fairly 



definite outer sphere. The sperm-nucleus occupies the same 

 position as before, and has undergone no change of structure ; 

 in Fig. 13 it is represented lying to the left. During the final 

 stages of formation of the second polar globule, the inner 

 sphere begins to enlarge, and the interior is occupied by a 

 reticulum, in the nodes of which are a number of centrosome- 

 like bodies. After the second polar globule is fully formed, 

 the sphere enlarges with great rapidity (Fig. 14), and, as its 

 boundary spreads out, it becomes less and less definite, until 

 its substance merges with the general cytoplasm. During its 

 enlargement, the interior is occupied by a vesicular substance, 

 at the nodes of which are deeply staining granules, in no wise 

 distinguishable from microsomes. The substance of the inner 

 sphere is now, in fact, part of the general cytoplasm. Yolk- 

 granules are entirely absent in it (Fig. 15), and this enables one 

 to follow its subsequent fate for a considerable period of time. 

 We shall call this substance, provisionally, spJierc-substance, 

 following Conklin (4); it is important to remember that it is 

 derived entirely from the inner sphere of the second maturation- 

 spindle. Either this is the case, or else the apparent enlarge- 

 ment of the inner sphere at the close of the maturation is due 



