WENRICH: SPERMATOGENESIS OF PHRYNOTETTIX MAGNUS. 105 
As to which of the two maturation divisions is equational and which 
is reductional, no absolute rule can be laid down. The evidence, 
however, points to the probability that generally chromosomes with 
terminal spindle-fiber attachment are not separated from each other 
until the second division, while those that have a non-terminal at- 
tachment are separated in the first, and that consequently in the 
former the reduction occurs at the second division, in the latter at the 
first division. 
B. INpDIvIDUALITY. 
The theory of individuality was early championed by Van Beneden 
(’83), Rabl (’85), and Boveri (’88). In more recent years the theory 
has been supported by many writers, who have accepted as substan- 
tial evidence in its favor the constancy in the number, size, and 
shape of the chromosomes reappearing in the mitotic spindle of any 
one species of animal or plant. On the other hand, some eminent 
zoologists have attacked the theory on the ground that the individual 
chromosomes cannot be traced through the so-called “rest”? period 
between mitoses. It will, therefore, be convenient to discuss the two 
topics: — (a) constancy in metaphase chromosomes, and (b) persistent 
organization of chromosomes. 
a. Constancy of Metaphase Chromosomes. 
1. Constancy in number.— The constancy in number of chromo- 
somes for any species is among the most commonplace of cytological 
observations. It will therefore be unnecessary to make any exten- 
sive references to the literature. Some exceptions to the general 
rule occur, however, and should receive attention. Supernumerary 
chromosomes have been reported from time to time, and have been 
studied especially by Stevens and Wilson. Wilson (’09) found in 
Metapodius variations in chromosome-number from 21 to 26, though 
the number for each individual animal was constant. The number of 
chromosomes was dependent neither on sex, nor locality of habitat, 
nor was it correlated with constant differences of size or of visible 
structures in the adults. But the variation affects only particular 
classes of chromosomes (the small idiochromosomes) and all exhibit 
the same behavior. Furthermore, Wilson found a few cases of mitoses 
in which both members of a pair of small chromosome were going to 
