104 Mr Doncaster, On the Maturation and Early Development 



before, giving rise to four nuclei which differ from those of the 

 other species in being of different sizes. The outermost is 

 smallest, the second larger, and the two inner ones larger still. 

 There is a considerably greater space between the two inner polar 

 nuclei than in the male-producing species, and these two nuclei 

 show no tendency to conjugate. The egg-nucleus sinks in and 

 begins to divide, and the polar nuclei move slowly to the edge of 

 the egg, begin to shrivel, and finally degenerate, usually without 

 showing any signs of breaking up into chromosomes. In some 

 eggs, however, at a stage at which in normal eggs the polar nuclei 

 would have nearly or quite disappeared, a compact mass of chro- 

 mosomes is found in the "polar protoplasm," and it seems probable 

 that in these rare cases a fusion of all three polar nuclei has taken 

 place, as was found by Henking in certain insects. 



In Hemichroa rufa, which produces mostly females with a few 

 males from unfertilized eggs, the course of events does not differ 

 greatly from that in P. luteolum. The polar nuclei are all about 

 the same size, and the two outer degenerate rapidly; the inner- 

 most on the other hand becomes resolved into chromosomes which 

 persist for some time without undergoing further change. As in 

 P. luteolum the two inner polar nuclei lie far apart, and show no 

 tendency to conjugate. 



Croesus varus produces only females from unfertilized eggs, 

 and the male is not certainly known. The earliest stages obtained 

 of this species were after the second polar mitosis, and show the 

 two inner polar nuclei in the polar protoplasm, and the degenerat- 

 ing remains of the outermost. The two inner polar nuclei are 

 very close together, as if preparing to conjugate, but the next 

 stage shows that one of them has become resolved into chromo- 

 somes, while the other has disappeared. The chromosomes derived 

 from the innermost polar nucleus (nucleus of the second polar 

 body) are at first eight in number, but before they degenerate 

 they divide so that at a later stage a greater number is found, as 

 was frequently the case in N. ribesii and N. pavidus. 



It appears therefore that in the arrhenotokous species the 

 inner daughter nucleus of the first polar body conjugates with the 

 second polar nucleus, the conjugation being more or less complete 

 in different cases ; in the thelytokous species, on the other hand, 

 no tendency to conjugation between these nuclei is observable, 

 unless their close proximity in G. varus indicates an abortive 

 attempt at conjugation in that species. It is of interest in this 

 connexion that in a very small proportion of eggs of N. ribesii, as 

 was mentioned in my previous note, the development takes place 

 after the thelytokous type, and it is known that a small percentage 

 of females may be bred from virgin eggs of that species. 



In my note on N. ribesii it was mentioned that the chromo- 



