L. DONC ASTER 195 



than in Pieris, and it was not easy to find examples cut so that the 

 chromosomes could be counted with perfect accuracy. Counts were 

 always made by drawing the chromosome group, not by eye. In the 

 most satisfactory figures the number appears to be 56, i.e. twice the 

 number found in the spermatocyte divisions. Two of these equatorial 

 plates are figured in Figs. 10 and 1 1 ; the only doubt about the number 

 56 in these cases consists in the facts that in Fig. 10 a pair of chromo- 

 somes (at the left upper edge, apparently consisting of a larger and 

 smaller member) might possibly be two halves of a dividing chromo- 

 some, but the only reason for this suggestion is that they are at slightly 

 different levels; and in Fig. 11 the double body outside the circle at 

 the bottom might conceivably not be a chromosome, for other stained 

 bodies occur in the cytoplasm outside the spindle. Careful examination 

 has convinced me, however, that in fact there are 56 in each figure. 

 The same number has been found in three other figures in which the 

 number 56 is quite clearly seen, and in a further three in which part 

 of the equatorial plate was seen in the next section to the main group, 

 so that a chromosome might possibly be cut so as to appear in two 

 sections, although this is very improbable when they are so small. 

 In a number of other figures it was impossible to decide with certainty 

 between 56 and 55, and in some only 54 were clearly visible. 



Since in the best figures obtained there is no reasonable doubt that 

 56 is the true number, and since an even number is certainly present 

 in Pieris brassicae, it may be concluded with some confidence that iu 

 the female Abraxas grossulariata the unreduced number of chromo- 

 somes is 56. 



With regard to the variety lacticolor I am less certain ; in all my 

 figures of this form counts may be interpreted as 55 or 56, according 

 to whether a double chromosome is regarded as one or two. As de- 

 scribed in my paper on the spermatogenesis, the lacticolor male does 

 not dififer recognisably from the grossulariata ^ in its chromosome 

 group, the spermatocyte number being 28 in each. It is to be ex- 

 pected therefore that the number in the female should not differ from 

 that of grossulariata. That the number in lacticolor is either 55 or 56 

 is certain ; a final decision on the matter can only be arrived at when 

 more material is available. It should be said that the chromosomes of 

 the oogonial divisions in both forms are not all equal in size ; in some 

 cases two are noticeably larger than the others, but these two are not 

 always recognisably different from the next in size, so that accurate 

 identification of chromosomes is hardly possible. 



