102 



Mr. L. Doncaster. 



[Sept. 21, 



like thaL found in the Bee, except that the nucleus returns to a " resting " 

 condition. 



4. The spermatocytes now develop about 20 chromatin masses which form 

 themselves into 10 band-like chromosomes. These shorten, form an 

 equatorial plate across the cell, a typical spindle is produced ; and the 

 chromosomes divide so that 10 travel into each daughter nucleus. Two 

 spermatids are produced, which are similar except that in some cases at least 

 one of them receives a small extranuclear body of unknown nature, which is 

 absent from the other. Both spermatids develop into spermatozoa. 



5. In primitive ova in the young female larvje of the summer generation, 

 mitoses like those in the body-cells are found, with apparently 20 chromo- 

 somes. After the deposition of yolk has begun, no further nuclear divisions 

 occur in the egg. 



6. The maturation divisions of the summer eggs are difficult to follow, 

 but apparently two divisions occur, giving rise to four groups of chromo- 

 somes, of which the three outer represent the three polar nuclei, while the 

 innermost group sinks in to form the female pronucleus. This group 

 probably consists of 10 chromosomes, but they are so crowded that the 

 number commonly appears rather less in sections. 



7. The male pronucleus and the female pronucleus meet and form the 

 first segmentation spindle, in which, as in the later segmentation divisions, 

 about 20 chromosomes appear. Tiie polar chromosomes disintegrate and 

 disappear. 



8. The pi-imitive ova of the spring generation have not been obsei'ved. 

 In an egg from the egg-tube of a young pupa 20 chromosomes were seen in 

 the nucleus. 



9. The maturation of the spring egg has not yet been sufficiently studied, 

 but it appears that some eggs undergo at least one maturation division, others 

 probably none. In eggs in which maturation has occurred segmentation 

 mitoses show 10 chromosomes ; all the eggs laid by one individual female 

 in which the chromosomes could be counted were of this type, and it is 

 suggested tliat these develop into males. In the eggs laid by other females, 

 however, 20 chromosomes appear in the segmentation divisions ; in these, 

 polar cliromosomes appear to be absent, and it is probable that there lias 

 been no maturation division, and that these eggs would develop inl,i) females. 



Most of the al)ove facts have been shortly discussed in the sections where 

 they are described, and only their more important general bearings remain 

 to 1)0 considered. Of these, perhajw the cbicif is the relation of the facts 

 observed in NauroicruH to what is already kiiovvTi in otlior Tlymenoptera, 



