152 GENERAL EMBRYOLOGY 



tion of chromosomes is fully accomplished in synapsis, before 

 the actual maturation divisions occur. For these and many 

 other reasons it seems that the chief importance of maturation 

 is from the standpoint of inheritance. This is true particularly 

 of most of the details regarding chromosome reduction, which 

 become significant only when correlated with the facts, first, 

 that the germ cells are the simplest phases in the life cycle of 

 the organism, alternating with the mature phases, the complex 

 characteristics of which are related to the simpler characters 

 of the germ, and second, that in some way, as yet unknown, 

 the structural and physiological characteristics of the new 

 organism are, at least in part, primarily determined by the 

 chromosomal structure of both of the germ nuclei, i.e., to the 

 fact of biparental inheritance. From the standpoint of in- 

 heritance then the details of the behavior of the chromosomes 

 during the maturation divisions take on the greatest importance. 

 One of the more important matters is the precise plane of 

 division of the chromosomes. It seems necessary to assume 

 that each chromosome is not entirely homogeneous, but that 

 its qualities differ in different parts. Consequently, in chromo- 

 somal composition the four nuclei derived from each primary 

 oocyte or spermatocyte nucleus may be all alike or may be of 

 different kinds, according to whether the original chromosomes 

 separated into similar or dissimilar parts in one or both of the 

 maturation divisions (Fig. 80) . In those cases where the chromo- 

 somes separate into qualitatively similar halves the division 

 is said to be equational, and when into qualitatively unlike 

 halves the division is reducing. And it is commonly believed 

 that one of the maturation divisions is equational and one re- 

 ducing. When the equational division precedes, post- 

 reduction is said to occur; when the reducing division precedes 

 it is described as prereduction (Korschelt and Heider). It is 

 by no means a simple matter to determine whether a given 

 chromosome division is equational or reducing, since there is 

 externally visible no indication, in a chromosome itself, of its 

 qualitative differentiation; and further because the processes 

 of rearrangement and redistribution of the chromatin granules 



