476 Early Development of the Unfertilized Egg in the Saw fly. 



soon the yolk contains a number of scattered nuclei, each em- 

 bedded in a little mass of protoplasm. The spindles of division 

 are extremely small, but in the few cases where I have been able 

 to count the chromosomes they appear to be about eight, i.e. they 

 remain at the reduced number. But the reticular nuclei imme- 

 diately after division contain a number of deeply-staining granules, 

 often about twenty, and it seems possible that this appearance has 

 led to the statement of Petrunkewitsch, that in the bee the 

 chromosomes of the egg-nucleus automatically become doubled. 

 The nuclei in the yolk increase rapidly, and at about the tenth 

 hour begin to come to the surface and form a blastoderm, but the 

 time of its first appearance varies greatly with the temperature. 

 Only in the blastoderm nuclei have I seen anything like a 

 nucleolus. 



Of eggs from impregnated females my series is not yet com- 

 plete, and unless the male pronucleus can be found it cannot be 

 proved that the egg is actually fertilized, even though the female 

 sawfly has been seen to copulate. The early stages appear to be 

 quite similar to those of the virgin egg, but in the third and 

 subsequent hours the chromosomes derived from the conjugating 

 polar nuclei, instead of forming fairly definite compact groups, are 

 usually scattered quite irregularly in the polar protoplasm, and by 

 the sixth hour appear to be disintegrating. In these eggs I have 

 not yet found a mitosis of a yolk-nucleus in which the chromo- 

 somes can be counted, nor have I been able to observe the fusion 

 of male and female pronuclei. 



The work is still very incomplete, since the early stages of the 

 fertilized egg have not yet been fully followed, and in no case has 

 the fate of the polar nuclei been traced beyond the beginning of 

 the blastoderm stage. It would therefore be premature to discuss 

 the meaning of the facts observed, but incomplete as they are they 

 are of interest from their remarkably close resemblances to the 

 processes observed by Petrunkewitsch in the bee. The chief 

 differences are that in the sawfly the maturation divisions take 

 place in the dorsal instead of the ventral side of the egg, and that 

 the "copulation-nucleus" does not divide to form a group of 

 nuclei, but forms instead groups of isolated chromosomes. 



In conclusion I may mention that in the few eggs of other 

 species which I have obtained, viz. N. pavidus and N. lacteus, the 

 development appears to be closely similar to that described in 

 N. ribesii. Of these species the first certainly and the second 

 probably belongs to the group in which virgin eggs yield males. 



Finally I wish to express my gratitude to Miss E. F. Chawner, of 

 Lyndhurst, for sending me a large and varied supply of larvae ; 

 without her assistance the work could hardly have been under- 

 taken. 



