No. 577] SHORTER ARTICLES AND DISCUSSION 



43 



females) for the combinations NynY and MYmy. As stated in 

 my former review, there was in the earlier paper a record of the 

 mating sysy £ X SysY J 1 , giving no cross-overs in 128 offspring. 

 Tanaka now says, referring to this case: "Whether there may 

 exist, in certain occasion, a complete reduplication [linkage] in 

 male, or whether the above result is due to any mistake by which 

 sex-signs have been reversed, is at present uncertain. No similar 

 case has as yet been found in other families." 



The evidence seems to make it highly probable that crossing 

 over in the silkworm moth occurs only in the male ; a surprising 

 result when we remember that in Drosophila it occurs only in the 

 female. One is immediately reminded that in Drosophila the 

 male is heterozygous for the sex-differentiator, while in Abraxas 

 and probably all moths the female is the heterozygous sex. These 

 facts are highly suggestive, and lead one to wonder what will be 

 found with regard to crossing over in the two sexes in birds and 

 mammals, where similar differences in sex-determination occur. 

 Another point worth noting in this connection is that in the 

 hermaphroditic sweet pea and Primula crossing over occurs in 

 the formation both of pollen and of ovules. 



Tanaka reports two cases of aberrant results which, as he says, 

 may be explained as due to mutation ("dropping out") of S in 

 one case, and of both S and Y in the other. He adds that such 

 an assumption is premature. To the writer it seems more prob- 

 able that the females involved were not virgin. The results are 

 easily explained on the assumption that they had paired with 

 brothers before isolation, since brothers of the necessary composi- 

 tion are shown by the pedigrees to have been present in each case. 



Another interesting point brought out by Tanaka 's more re- 

 cent paper is the relation between the larval patterns known as 

 striped, moricaud, normal, and plain. In my earlier review I 

 followed Tanaka in treating these patterns as affected by three 

 pairs of genes: S (striped) and s, M (moricaud) and m, and 

 N "(normal) and n, plain being the triple recessive. The same 

 scheme has been followed in the early part of this paper. On 

 this assumption, as Tanaka points out, it is necessary to suppose 

 that complete linkage occurs between these three pairs of genes. 

 The evidence need not be gone over in detail here, but there are 

 over 10,000 larvae recorded from various tests of this relation, 

 without a single cross-over among them. Although Tanaka does 

 not mention the point, this at once brings up the possibility that 



