122 KATHARINE FOOT AND E. C. STROBELL. 



two spermatogonial chromosomes and not one, and when this 

 chromosome is first formed its bivalent character is much more 

 pronounced than at the later prophase stages. Our photographs 

 however support Wilson in his claim that it appears only excep- 

 tionally as a tetrad - - as a rule this and the micro-chromosomes 

 appear bivalent, while all the others show a marked tetrad char- 

 acter. The frequent eccentric position of this bivalent chromo- 

 some, outside the characteristic ring arrangement of the chro- 

 mosomes in the late prophase, seems to warrant suggesting 

 "eccentric" chromosome as a convenient descriptive name for 

 this special chromosome. 



Individuality of the Chromosomes. Our preparations show a 

 marked individuality ot the chromosomes, and in this support 

 the observations of Paulmier, Montgomery and Wilson. Sev- 

 eral of the chromosomes can often be clearly identified during 

 the prophases, metaphase and anaphase, though a comparison of 

 a large number of photographs demonstrates that \\\z form is not 

 constant. For example, at a definite prophase, 7, 8 or 9 of the 

 1 1 bivalents may be clear and sharply defined crosses, while 

 again in the same stage we may have all rods or only I, 2 or 3 

 crosses, this indicating that the cross type is not invariably asso- 

 ciated with any one chromosome. 



During the growth period the chromosomes certainly lose 

 their individuality as completely as in the case of Allolobophora 

 fcetida, and we have therefore no positive proof that each biva- 

 lent of the prophase represents the same chromatin that formed 

 a pair of the spermatogonial univalents. There is a certain 

 degree of constancy in the relative sizes of the chromosomes, 

 although a definite chromosome may differ greatly in size in dif- 

 ferent cells at the same stage of development. This may be due 

 in some degree to the technique, but this difference is often so 

 great that we feel convinced it is probably due at least in 

 part, to an actual difference in the size of the individual chromo- 

 somes. 



Montgomery ('06) observed an inequality in the size of the 

 two microchromosomes, but in our preparations we do not find 

 any support for this observation. 



Plane of the First Division. In many cells in which all the 



