10 Chromosomes and Sex in Abraxas 



seems to be somewhat more frequent ; I have counted ten figures with 

 28 separate chromosomes, and eight in which two are associated. The 

 degree of association varies somewhat, and in a few cases, especially in 

 one male of '12.7, the two are so close together that they might eiisily 

 be mistaken fur one. This is not the case in any of the figures from 

 the .55-chromosome strain, and since such a double chromosome is not 

 found in figures in which 2lS separate chromosomes ai-e seen, and since 

 the two members of the pair are not always equal in size, I think it is 

 certain that 2(S is the number constantly found in all seciiiidary sper- 

 matocytes. In Biston hirtmia I have found that in the si^eruiatDcytes 

 two chromosomes are constantly associated, and the occasional figures 

 which might be counted as 27 in Abraxas are probably due to the less 

 regular occurrence of the same sort of thing. 



The spermatogonial divisions are not usually clear enough to give 

 quite reliable counts. I have nuxde very many attempts, and in almost 

 all the best figures I have found .56, whether of the strain with 55 in 

 the female or in males not belonging to this strain. I have altogether 

 twenty spermatogonial figures recorded as ' good ' or ' very good ' in 

 males belonging to the strain in which the female has 55 ; of these 

 sixteen show 56, three might be either 56 or 55, and one shows only 55. 

 All the six best figures have clearly 56 (Fig. 9). I have thereft)re no 

 hesitation in concluding that in all males 56 is the spermatogonial 

 number, and that all spermatozoa contain 28. 



d. The Maturation Divisiovs of the Er/tjs. 



The polar divisions take place in a little patch of protoplasm at 

 the anterior end of the egg, and in searching for them in sections the 

 anterior end can usually be recognised by the somewhat finer granu- 

 lation of the yolk. During the maturation, the superficial protoplasmic 

 layer of the egg is drawn out, just at the point where the outer polar 

 nucleus will lie, into a fringe which in sections has exactly the ap- 

 pearance of a tuft of cilia (Fig. 14) ; this usually makes the division- 

 figures easy to find in a longitudinal section, but is of no help in 

 sections transverse to the axis of the spintUes. I have not discovered 

 the meaning of the fringe ; it is possibly due simply to the superficial 

 protoplasm sticking to the shell at the point where the polar divisions 

 occur. During the maturation divisions, the heads of the spermatozoa, 

 with their radiations, are usually conspicuous objects in the jolk near 

 the anterior pole. One can almost always be found, and not rarely one 

 fir two others are present in addition. I cannot give the exact times 



