198 Chromosomes in Pieris and Abraxas 



chromosomes in the earlier stages of oogenesis therefore do not pro- 

 vide any visible basis for the sex-limited transmission of characters. 

 If Spillman's suggestion be correct, that in the normal grossulariata 

 male there are two G-bearing chromosomes, while in the female one 

 of these is replaced by a sex-chromosome {"X ") which does not bear 

 G (the factor for grossulariata), this is what would be expected ; but 

 since, in the male at least, the variety lacticolor has the same number 

 of chromosomes as grossulariata, the G'-bearing chromosomes would 

 have to be supposed capable of losing the factor G without becoming 

 visibly different. 



Note. — Since the above was written, I find that Payne (Journ. 

 Morphol. Vol. XXIII, 1912, p. 331) has come to conclusions closely 

 similar to mine about both the constitution of the nucleolus and the 

 origin of the oocytes in Reduviidae ; and Miss P. H, Dederer has 

 published a preliminary note on the maturation of the eggs of Philo- 

 samia cynthia {Biol. Bull, xxill. p. 40, June 1912) in which she finds 

 no dimorphism among the egg- chromosomes. 



Postscript, Sept. 26, 1912. 



In ovaries of larvae derived from the 1912 pairings, although I have 

 no perfectly trustworthy figures in individuals derived from the cross 

 lact. X lact, I have several which show 56 chromosomes quite clearly in 

 larvae from the cross gross. $ x lact. cf. Since this cross always gives 

 only lacticolor females, it may be concluded with confidence that the 

 chromosome number in the lacticolor female is not dififereut from that 

 in the grossulariata female. 



EXPLANATION OF FIGURES. 



All the figures except 13a were drawn from sections stained with iron-haematoxylin ; 

 for all Zeiss apochromat n. a. 1.40, 3 mm. and oc. 12 were used. 



In figs., 3, 4, 5, 13a, 15a the shaded area round the nucleolus represents the non- 

 chromatic portion from which chromatin stains are easily washed out. 



Figs. 1 — 9. Pieris brassicae. 



1. Oogonial division, equatorial plate. 



2. Synizesis stage. 



3. Shortly after synizesis. The upper half of the nucleus is not included in the 



section. 



4. Rather later stage ; complete nucleus with 14 threads and chromatin-nucleolus. 



5. Contraction of threads to form double chromosomes ; only 13 of these are visible 



in this nucleus, the fourteenth is probably hidden by the nucleolus. 



