Smallwood. — Maturation Hamiuea. 



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 cliromosomes having divided. The egg 

 chromosomes in Figure 38 are surrounded by a nuclear membrane, 

 with which they are connected by linin fibres. At both poles of the 

 spindle, tiie centrosome contains two centrioles joined by a central 

 spindle. Iron htematoxylin 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 ha3matoxylin and Bordeaux red. 



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

 brane and linin fibres. A thin-walled vesicle without chromosomes 

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

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

 which has become broken and less distinct. Tlie new centrosomes 

 have accumulated around themselves a cortical layer of sphere-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 hajmatoxylin 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 the metaphase. The 

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

 the raj's 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 the old sphere-substance being well marked. The accessory 

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

 brane. Iron haematoxylin 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 htematoxylin. 



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

 animal pole. The boundary of the old centrosome much 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 sphere-substance have become limited to the deep 



