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 /j, in length, which contains a bright, highly- 

 refracting nuclear particle, the head 2 yu, 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 Tachinae for my observa- 

 tions. I have no doubt, however, that the spermatozoids of 

 the Blow-fly are active when they are discharged from the 

 spermathecae at the moment of the fertilisation of the ova. 



