Small WOOD. — Maturation Haminea. 



PLATE 7. 



All figures magnified 1224 diameters. 



Figs. 38, 39. Radial sections through the animal pole of the egg. First matura- 

 tion spindle in anaphase, the chromosomes having divided. The egg 

 chromosomes in Figure 38 are surrounded by a nuclear membrane, 

 with wliich they are connected by liuin fibres. At both poles of the 

 spindle, tlie centrosome contains two centrioles joined by a central 

 spindle. Iron haematoxylin and Bordeaux red. 



Fig. 40. First polar cell formed. The egg chromosomes have become vesicular 

 and are joined to the nuclear membrane by linin fibres. In both Fig- 

 ures 39 and 40, the bounding wall of the centroplasm of the egg 

 . centrosome is no longer continuous, being broken at several points ; 

 beginning of its disintegration. The centrioles are connected by a 

 central spindle. Iron haematoxylin and Bordeaux red. 



Fig. 41. Egg chromosomes separated into two clusters, each with a nuclear mem- 

 brane and linin fibres. A thin-walled vesicle witliout chromosunies 

 Hes near the periphery of the egg, almost in contact with the parent 

 centrosome, which has increased in size, and the degenerating wall of 

 which has become broken and less distinct. The new centrosomes 

 have accumulated around themselves a cortical layer of spliere-sub- 

 stance, in which new short radiations are established ; spindle much 

 elongated. Old radiations, centering in the enlarged parent centro- 

 some, have not entirely disappeared. Iron haematoxylin and Bor- 

 deaux red. 



Fig. 42. Achromatic figure of second maturation spindle larger, although the first 

 polar spindle has advanced only to the close of tiie metaphase. Tlie 

 wall of the parent centrosome, though conspicuous, is interrupted ; 

 the rays of the new centrosomes more prominent and longer than 

 in Figure 41; those of the parent centrosome still conspicuous and 

 extensive, the contrast between the cortical and medullary portions 

 of tlie old sphere-substance being well marked. The accessory 

 chromosome of the first spindle is partly enveloped in a nuclear mem- 

 brane. Iron hjematoxylin and Bordeaux red. 



Fig. 43. First polar cell already formed. Chromosomes vesicular, though not 

 yet surrounded by a nuclear membrane, and some of them connected 

 with linin fibres. The new centrosomes of the second spindle some- 

 what larger than in Figure 42, and a greater accumulation of new 

 sphere-substance about them. Iron hematoxylin. 



Figs. 44, 45. Achromatic figure enlarged and moving into a radial position at the 

 animal pole. The boundary of the old centrosome mucli interrupted 

 in Figure 44, and wholly wanting in Figure 45. In Figure 44, the 

 central spindle is narrow and well defined; in Figure 45, it is more 

 swollen and spindle-shaped. In this figure medullary and cortical 

 layers of the old spiiere-substance iiave become limited to the deep 



