290 LILLIE. 



EXPLANATION OF PLATE XXVL 



Fig. 32. Telophase of the second maturation spindle. The inner sphere has 

 enlarged considerably, and in place of the single centrosome there are a number 

 of deeply staining bodies united by a delicate reticulum within the sphere. The 

 entire sphere stains more darkly than before. The aster shows the usual appear- 

 ance of degeneration, being thickly studded with large microsomes. 



Fig. -^y Beginning of reconstruction of the egg-nucleus. The inner sphere 

 has swollen up to a relatively enormous size, and is occupied by a loose-meshed 

 reticulum with deeply staining microsomes on the fibers. 



Fig. 34. The egg-nucleus has enlarged considerably, and the sphere substance 

 is continuous with the general cytoplasm. 



Fig. 35. Beginning of the migration of the germ-nuclei. The egg-nucleus, 

 accompanied by the sphere substance, is moving towards the side of the egg away 

 from the sperm-nucleus, which has taken up its march in the general direction of 

 the egg-nucleus. Zeiss 4/2 mm. Combination of four sections. 



Fig. 36. Similar section in a slightly later stage of the migration. In this 

 stage the sphere substance has elongated in a plane at right angles to a line unit- 

 ing the germ-nuclei and to the axis of the egg. Zeiss 4/2 mm. 



Fig. 37. Section in the plane indicated on Fig. 36 to show the elongation of 

 the sphere substance. 



Fig. 37a. Outline of sphere substance in a later stage stretching completely 

 across the egg. 



Fig. 38. Meeting of the germ-nuclei. This is the earliest stage in which the 

 cleavage centrosomes can be distinguished. The figure is a combination of two suc- 

 cessive sections ; hence the appearance of overlapping of the nuclei. The centrosomes 

 are therefore simply seen through the nuclei. They do not lie in thetn. For the sake 

 of clearness the chromatin has been omitted, except in the right-hand border of 

 the egg-nucleus. The latter can be distinguished from the sperm-nucleus by its 

 relation to the sphere substance, which can still be distinguished. 



Figs. 39-43. Illustrate origin of asters, spheres, and chromosomes of the first 

 cleavage spindle. The position of every chromatin granule and spindle fiber in 

 Figs. 39-43 is drawn in as accurately as possible. 



Fig. 39. Combination of two successive sections ; before the formation of the 

 central spindle. The centrosomes are broken into a number of parts imbedded 

 in a red-staining mass. Outer sphere well marked ; mag. Zeiss 8/2 mm. 



^Fig. 40. Slight advance in aster and spindle formation. First rudiments of 

 chromosomes may be distinguished ; mag. Zeiss 8/2 mm. 



Fig. 41. Origin of central spindle; chromosomes and mantle-fibers forming. 

 Notice chromatin masses near the centrosomes. Slight diminution in amount of 

 basichromatin. Zeiss 8/2 mm. 



Fig. 42. Combination of two successive sections. Great diminution in amount 

 of basichromatin ; long chromosomes appearing. Other chromatin granules in 

 spindle fibers, and yet others in the neighborhood of the centers. Remainder in 

 the form of oxychromatin (?). Zeiss 8/2 mm. 



Fig. 43. Early stage of the first cleavage spindle ; the two groups of chromo- 

 somes readily distinguished ; each chromosome is very long and delicate but 

 distinctly double. 



Fig. 44. Later stage of the first cleavage spindle before its shifting. Vesicular 

 " centrosome " (inner sphere). 



