DEVELOPMENT OF THE GENERATIVE ORGANS. 697 
that it would require many years devoted to the special in- 
vestigation of the subject and much preliminary work before 
any observations of value could be expected. 
The accessory nucleus (Nebenkern) in the developing sper- 
matozoa, which has been observed so frequently by various 
observers, is not visible in any of my preparations, but it 
apparently needs special methods for its demonstration; and 
whether it has any real existence, or is merely the result of the 
methods employed, remains doubtful. Oscar Hertwig, in his 
recent researches, has not confirmed its existence in the sense 
of Lee’s statements, although inert nuclei are observed and 
have been regarded by him as similar to the polar globules dis- 
charged from the ova. 
The whole of this intricate subject must be considered at 
present as unsettled, and will probably require many years 
before any final settlement is arrived at. 
The Mature Spermatozoa consist of extremely fine filaments, 
measuring nearly ‘25 mm. in length, with a thick elongated 
neck about 20 mw in length, which contains a bright, highly- 
refracting nuclear particle, the head 2 » in diameter. Such 
spermatozoa are found enclosed within the spermatic capsules 
of the impregnated female. 
The spermatozoa removed from the testis of the male do 
not exhibit active movements, and the long filament is often 
detached from the head and neck. The detached head and 
neck assumes the form of a spherical corpuscle. I formerly 
[1869] dissected a female fly, which had been some hours in 
spirit, in which I found the oviduct full of active vibrating 
spermatozoa. I supposed the insect had been captured imme- 
diately after union with a male, and that the spirit had not 
permeated it [62], but I have never seen anything similar 
since, nor am I sure that the insect in which I observed this 
phenomenon was Calliphora erythrocephala, as at that early 
period of my work I frequently used Tachine for my observa- 
tions. I have no doubt, however, that the spermatozoids of 
the Blow-fly are active when they are discharged from the 
spermathece at the moment of the fertilisation of the ova. 
