190 Chromosomes in Pieris and Abraxas 



account I shall describe first the behaviour of the chromosomes in 

 the oogenesis and spermatogenesis of Pieris brassicae in which the 

 phenomena are more easily followed, and then return to the oogenesis 

 of Abraxas. 



Pieris brassicae. 



Ovaries and testes were dissected out of fresh adult larvae and 

 young pupae (1 — 5 days) fixed immediately in Flemming's fluid, cut 

 into sections of about 6/i- in thickness, and stained with Heidenhain's 

 iron haeraatoxylin. Some also were stained with Breinl's process^ 

 for comparison, especially for the study of nucleoli. A point of some 

 interest is the fact that in adult larvae in August and September, 

 from which the imago will not emerge until the following spring, the 

 testes have attained their full size, and contain every stage of spermato- 

 genesis from spermatogonia grouped around a conspicuous Verson's cell 

 in each compartment to practically mature spermatozoa. The ovaries in 

 adult larvae, on the other hand, are extremely small, consisting of four 

 parallel tubes or rather columns of cells showing as yet no division into 

 egg-chambers, and with no deposition of yolk in the eggs. That almost 

 fully formed spermatozoa should exist in the larval testis before the six 

 months' hibernation of the pupa is a somewhat surprising fact. 



Oogenesis. In the tubes of the ovary — if they may be called tubes 

 when they are in no sense hollow — when the tube is cut longitudinally, 

 a continuous series may be seen from early oogonia through multipli- 

 cation stages to the earlier growth-phases of the oocytes before the 

 deposition of yolk. Since all the stages occur in fairly regular order 

 from the apex of the tube downwards, they are easier to follow than 

 are the corresponding stages of spermatogenesis, for in the testis the 

 cells are grouped in follicles which are very irregularly arranged. An 

 examination of the stages of spermatogenesis, however, shows that they 

 are closely similar to the series found in the egg-tubes. 



The apex of the tube is packed with small oogonia, of which the 

 nucleus in the resting stage shows a faint reticulum and a conspicuous 

 nucleolus. The latter in favourably-stained cells appears to consist of 

 a double or bilobed chromatin mass associated with a plasmosome, or 

 enclosed in a mass of achromatic material ; not infrequently the two 

 halves of the chromatin mass may lie apart, and sometimes appear 

 compound. Division figures commonly occur in groups; when equatorial 



1 Ann. Trap. Med. and Parasitology, Vol. i. 1907, p. 470. 



