L. DONCASTBR 183 



The later development of the small spermatids appears to be 

 identical, as far as I have been able to follow it, with that of the 

 " apyrene " type in Pygaera as described by Meves. When the 

 developing spermatozoa become aggregated in bundles, it may generally 

 be seen that these are of two sizes ; in the larger the nuclei are at one 

 end, being transformed into the heads of the spermatozoa, but in the 

 smaller the nuclei are scattered along the tails of the spermatozoa and 

 appear to be degenerating. A few such degenerating nuclei may some- 

 times be seen in the large bundles (Fig. 21, a, h). In teased prepara- 

 tions of the testes of the imago, the small spermatozoa in which the 

 nuclei have degenerated appear to remain in bundles, which suggests 

 that only the large nucleate ones are functional in fertilisation. This 

 is confirmed by sections of testes of the imago in which nearly all the 

 spermatozoa are of the small degenerate type, while in the vas deferens 

 nearly if not quite all are of the normal kind. Probably therefore the 

 degenerating spermatozoa do not leave the testis. In the imago the 

 degenerate spermatozoa are in the same stage as in the pupa ; I have 

 not seen the final stages leading to complete loss of the nuclei described 

 by Meves in Pygaera. 



In conclusion, it should be said that the observations here described 

 apply equally to pure (wild) grossulariata, to the variety lacticolor, 

 and to the heterozygote between the two varieties. The formation 

 of " apyrene " spermatozoa is thus not connected with the lacticolor 

 variety, and my observations do not give any indication of the cause 

 of the phenomenon. The suggestion of Meves that " apyrene " sperma- 

 tozoa are capable of fertilising an egg but not of transmitting the 

 paternal hereditary characters is not borne out by breeding experiments, 

 nor do these confirm the suggestion that the two types of spermatozoa 

 determine different sexes in the fertilised egg. 



I have only made a cursory examination of the mitoses in the 

 germ-cells of the female, but those in the egg-tubes (oogonia) of a 

 full-fed larva do not differ recognisably from the spermatogonia! 

 mitoses described above. 



