204 THOMAS H. BRYCE. 



longitudinal cleavage in the secoud metakinesis. The second 

 mitosis thus merely distributes the granddaughter chromo- 

 somes formed by the second longitudinal splitting in the first 

 mitosis. 



There is thus no " reducing division." The only reduction 

 which occurs is effected in the germinal vesicle, and the 

 chromatin destined to form the chromosomes of the polar 

 divisions is diminished in bulk merely. 



Critical Analysis of Results and Comparison with 

 those of other Observers. — In describing the achromatic 

 structures I have sufficiently indicated how the appearances 

 I have described in my material are to be compared with 

 those described by other observers. With regard to the 

 chromatin elements I may now give a further analysis. 



Glancing over the whole field of research on the subject 

 the first thing that strikes an observer is the remarkable 

 unity of the process, even in detail, over a very large range of 

 forms. The figures represented for the great majority of 

 both the higher plants and the Metazoa show resemblances 

 so close that one cannot imagine they are produced in one 

 way in one form and in another way in another form. 

 Interpretation and theoretical conclusions may differ, the 

 process is identical throughout. 



It has been insisted that the solution of the problem of 

 reduction lies in the determination of the origin of the 

 tetrads, but as these in typical form occur in a relatively 

 small number of cases, it seems that the solution rather lies 

 in a closer analysis of the heterotypical division, such as has 

 lately been done for plants by Strasburgcr. 



Heterotypical division was first described by Flemming, 

 in 1887, as a form of mitosis occurring in the spermatocytes 

 of the salamander, and in all cases in which tetrads are not 

 formed a heterotypical division in some sort ushers in the 

 first maturation division with its reduced number of chromo- 

 somes, and this is true of plants as well as animals. The 

 distinctive features of this division as originally stated are : 



1. The spireme stage is not so compact ;is in other kinds 



