RELATION BETWEEN AMITOSIS AND MITOSIS. 1 39 



of clearness, however, the two processes are described separately, 

 the figures being sufficient to show the conditions as regards 

 both maturation and fertilization at different stages. 



When the egg leaves the ovary on its way to the uterus it is 

 flattened or irregular in shape, without any visible polar differen- 

 tiation so far as could be discovered, and contains a large nucleus 

 with very large nucleolus. Within the nucleus all traces of the 

 spireme which appeared at the beginning of the growth period 1 

 have disappeared and except for the nucleolus the nuclear con- 

 tents, like those of many other egg-nuclei at this stage do not 

 take nuclear stains. 



Fig. 1 (PI. II.) shows an egg at this stage but with the sperma- 

 tozoon entering. In this egg two bodies shown below the 

 nucleus are probably the centrosomes of the first maturation 

 spindle, though it was impossible to be certain on this point. 



With the entrance of the spermatozoon a vitelline membrane 

 is formed (Fig. 2 et seq., PI. II.). Chromosomes soon begin to 

 form in the nucleus (Figs. 2 and 3, PI. II.). 



In Fig. 4 (PI. II.) an early stage of the first maturation spindle 

 is shown. Here the outline of the nucleus is still visible and the 

 spindle appears to be wholly intranuclear. The very large cen- 

 trosomes at the poles show a distinctly differentiated outer bound- 

 ary which appears almost like a membrane. One of them in this 

 figure shows two deeply staining granules, the other, none. 

 The appearance and division of these central granules, or centri- 

 oles, is seemingly rather irregular as the following figures indi- 

 cate. In no case has any trace of asters been observed at any 

 stage of maturation, but with the formation of the spindle, the 

 yolk spherules arrange themselves about the equatorial region. 

 This arrangement of yolk spherules indicates that conditions 

 about the poles of the spindles are similar to those in species 

 where distinct asters appear. It is probable that the absence of 

 asters is not due to any fundamental difference in the character 

 of the processes in this case as compared with cases where asters 

 are visible, but rather to the nature of the protoplasm or perhaps 

 to the energy of the processes involved. The achromatic spindle- 

 structures themselves are exceedingly delicate and often only 



2 Child, C. M., Biol. Bull, XII., 2, 1907. 



