CHROMOSOME COMPLEX OF SPERMATOCYTES. 339 



mental differences. Therefore it appears that the fluctuating 

 variations which occur in a series of organisms comprising a 

 species are the results of minor differences in the chromosomes of 

 the germ cells, due to the impossibility of exactly duplicating the 

 conditions of union and separation of the paternal and maternal 

 chromosomes in maturation. 



Mutations on the other hand follow some unusual disturbances 

 in the relations of chromosomes to each other, brought about 

 by some change in the germ plasm whose cause we cannot now 

 determine. So much, I believe, we may conclude from our 

 present knowledge of the germ cells and their behavior in matura- 

 tion and fertilization. As our detailed knowledge of the chromo- 

 somes increases we may be enabled to speak more definitely and 

 certainly, but further information we must have and it is earnestly 

 to be hoped that the chromosome groups of many species of 

 these Orthoptera may be carefully and exhaustively studied in 

 connection with observations upon body variation so that corre- 

 lation between the two may be established. 



ZOOLOGICAL LABORATORY, UNIVERSITY OF KANSAS, 

 June 21, 1905. 



NEW TERMS EMPLOYED. 

 Definitions and Classifications of C/ironioscmcs. 



Chromosomes are chromatin elements acting as unit structures 

 during mitosis. 



Chromosomes are of two general classes. 



1 . Simple containing two chromatids in metaphase. 



2. Multiple containing more than two chromatids in meta- 



phase and formed by the union of simple chromosomes. 

 (a) Tetrads, containing four chromatids. 

 (//) Hexads, containing six chromatids. 



(c) Octads, containing eight chromatids (not yet observed). 



(d] Decads, containing ten chromatids. 



A chromatid is a half of a simple chromosome. 



"Synizesis"- -the unilateral or central contraction of the chro- 

 matin in the nucleus during the prophase of the first spermatocyte. 

 A term proposed to avoid the misuse of the word "synapsis." 



