92 CYTOLOGY 



CHAP. 



male nucleus, and there forms the first cleavage spindle of the developing 

 embryo. 



Great interest attaches to the cytology of the spermatogenesis of the 

 individual developing from these eggs, for since it is already haploid 

 a further reduction of chromosomes must be avoided. How this is 

 accomphshed has been worked out by Meves. 



The main features of the meiosis in the drone are shown in Fig. 43. 

 None of the usual meiotic prophase stages, such as leptotene or zygotene 

 nuclei, are found ; no essential stages seem to intervene between that 

 shown in Fig. 43, A, and that of Fig. 43, B, by which time the definitive 

 chromosomes have appeared. There are sixteen of these as in the 

 spermatogonia, each being conspicuously split longitudinally. An 

 intra-nuclear mitotic figure is formed and the chromosomes congregate 

 at the equator as if for an ordinary metaphase. This, however, is not 

 consummated ; the daughter chromosomes do not separate, but the 

 mitotic figure degenerates and the chromosomes become clumped together 

 again, generally at one pole of the elongated nucleus. Although the 

 nucleus does not di\ade, cell di\dsion proceeds, with the result that one 

 of the daughter cells lacks a nucleus. The non-nucleated cell is very 

 much smaller than the other, and of course takes no further part in 

 gametogenesis. Meanwhile the nucleus of the other cell prepares for the 

 second meiotic division, sixteen chromosomes again appearing as in the 

 abortive first division. The second division is carried through in the 

 normal way in so far as the nucleus is concerned, each chromosome 

 dividing into two daughter chromosomes which separate in anaphase. 

 Curiously enough, however, the cell again di\ndes very unequally, though 

 this time both daughter cells receive a nucleus. These of course each 

 contain sixteen chromosomes (though here again they tend to come 

 together in eight pairs — see footnote to p. 91). 



In spite of their unequal size, both spermatids begin the series of 

 changes which should convert them into spermatozoa, but it is probable 

 that only the larger one completes the process. 



The essential feature of this spermatogenesis is of course the omission 

 of the true meiotic division, by which a further halving of the already 

 haploid group of chromosomes is avoided. In conformity with this, no 

 such stages as leptotene or zygotene nuclei have been described in the 

 male honey-bee. That these stages are really absent is made still more 

 probable by Armbruster's (1913) observation on the spermatogenesis 

 of the soHtary bee Osmia cornuia. He states that though he specially 

 looked for these stages he failed to find them ; the telophase of the 

 last spermatogonial division appears to pass without important inter- 

 mediate stages into the diakinesis of prophase I. 



The unequal cell division of the secondary spermatocyte in the honey- 



