112 N. M. Stevens 



must be the result of fertilization by spermatozoa which contain 

 either no heterochromosome or the smaller of an unequal pair. 



The only other alternative for these insects seems to be that sex 

 is already determined in the egg before fertilization either as a 

 matter of dominance or as a result of maturation, and that fertiliza- 

 tion is selective; i.e., the eggs that are already predetermined to 

 produce females can be fertilized by those spermatozoa only which 

 contain the odd chromosome or the larger of two unequal hetero- 

 chromosomes, while the eggs which are already male can be ferti- 

 lized only by the other class of spermatozoa. If a general appli- 

 cation of the results obtained in insects were to be made, the second 

 supposition would certainly cover more cases, but any such general 

 application is premature until adequate evidence is at hand to 

 prove that the sex character is represented in the chromosomes. 



Further study of the phenomena of synapsis and synizesis in the 

 Coleoptera indicates the existence of at least two distinct types. 

 In the first, which I have called the loop type, synizesis seems to be 

 a prolonged telophase of the last spermatogonial mitosis, the sper- 

 matogonial number of chromosomes appearing as short loops 

 crowded together at one end of the nucleus. After a time the 

 loops straighten and the free ends unite in pairs and the pairs 

 unite to form a spireme. In some cases the synapsis stage is very 

 distinct, in others, synapsis and union to form a spireme occur 

 nearly or quite simultaneously. 



The second, or spireme type of synizesis is preceded by synapsis 

 which may form a distinct stage as in Photinus pennsylvanicus and 

 Limoneus grisens, or it may occur in the anaphase or telophase of 

 the last spermatogonial mitosis, and a closely wound spireme 

 follow immediately. In this type, the heterochromosomes are 

 usually distinguishable in the synizesis stage outside of the massed 

 spireme, while in Type I they are not seen until after the spireme 

 is formed. 



Bryn Mawr College 

 March 4, 1908 



