542 P. W. WHITING 



member of each pair separate at one or both ends and each 

 unites with a chromatid from the other member. When this 

 occurs at one end a cross is formed; when at both ends, a ring. 

 A process comparable to this occurs at earlier stages in which 

 the chromatids 'change partners' in part or all of their length. 

 It is thus impossible to say whether the first spermatocyte 

 division is reductional or equational. 



In the second spermatocyte prophase the chromosomes appear 

 as three pairs of rods, the members of which separate in ana- 

 phase. Three chromatids go to each spermatid. 



The spindle fiber attachment is approximately at the middle 

 of all chromosomes. In the tetrads it is attached to the middle 

 of each chromatid. 



A distinct nucleolus always appears between successive dip- 

 loid mitoses and in the growth stages of the first spermatocyte. 



It often shows four darkly stained regions. These nucleolar 

 elements are separated at certain stages. Two of them appear 

 to form terminal granules on one of the larger chromosome pairs, 

 while the other two are connected with the middle of the same 

 pair. 



In the second spermatocyte interkinesis and in the spermatids, 

 two nucleoli of constantly unequal size appear. In the second 

 spermatocyte the smaller nucleolus becomes the terminal gran- 

 ules of one of the larger pairs, while the larger nucleolus becomes 

 diffuse and disappears. 



111. DISCUSSION 

 A. INTRODUCTORY 



It will now be of interest to consider the causes for the wide 

 difference of opinion prevailing among the investigators of Culex 

 pipiens. This diversity is not merely a matter of interpretation; 

 it concerns facts. The number of chromosomes, the normal 

 occurrence of synizesis, the nature of synapsis, as well as the 

 much discussed matter of chromosome individuality are all 

 questions in regard to which the observations seem to differ. 



