SEGREGATION OF HOMOLOGOUS CHROMOSOMES 459 



cording to size is only a rough estimate. Numbers 1, 2 and 4, 1 

 feel sure, are correctly identified in all cases, but aside from these 

 there are scarcely any two consecutive ones which might not 

 exchange places, yet the extremes are clearly distinguished. As 

 the chromosomes are arranged, numbers 10, 11 and 12 are rings 

 of the Stenobothrus type in all cases. I am inclined to think 

 that this is correct. However, chromosome number 9 of the 

 fifth animal might well change places with number 11. I have 

 not been able to estimate satisfactorily the quantity of chromatin 

 in the rings. On the other hand, it is readily seen on the slides 

 that a given chromosome may be stretched out considerably with 

 a comparatively slight thinning to compensate. The difference 

 between an early and a late metaphase is also very striking. In 

 the former the chromosomes are short and thick while in the 

 latter they are evidently coming under some force which 

 tends to stretch them out along the spindle axis. There is some 

 evidence that this force is exerted through the spindle fibei s ; for 

 instance', the accessory in individual number 45 (plate 7) has nu- 

 merous fibers from both poles attached to it and its appearance 

 certainly indicates that force is being exerted at the points of 

 attachment. 



It will be noted from the foregoing that any J-shaped tetiad 

 has the capability of appearing in other individuals as a chromo- 

 some of either the Stenobothrus or Hippiscus type. Using this 

 knowledge as a key, it is evident from a study of animals num- 

 ber 3 and number 32 (plates 2 and 5) that all of the chromo- 

 somes except number 2 and number 3 possess the potentiality 

 of being of the Stenobothrus type in other individuals. If we 

 then follow chromosomes number 2 and number 3 through the 

 plates, we find chromosome number 3 in individual 16 (plate 3) 

 to be a J, and in individual 21 (plate 4) we get the combina- 

 tion of two atelomitic homologues giving a Stenobothrus tj^pe of 

 tetrad. Again, in individual number 31 (plate 5) it is a J. It is 

 also of this form in animals number 7 (plate 2) and number 22 

 (plate 4). Chromosome number 2 does not occur except as a 

 tetrad of the Hippiscus type in my collection. There was some 

 fear that I might be confusing chromosomes number 3 and 



