ZOOLOGY AND BOTANY, MICROSCOPY, KTC. 301 



distinguishable, but a count was not possible. The resting nucleus of 

 the primary spermatocyte contains a large chromatin nucleolus. The 

 conjugation of the chromatin threads takes place by parasynapsis. 

 The chromosome nucleohis presents itself throughout the synapsis and the 

 growth stages. In the primary spermatocyte the idiozome is conspicu- 

 ously present. The number of chromosomes in the first division is nine- 

 teen — namely, eighteen bivalent and one accessory. The first division 

 is reducing and heterotypic. The accessory chromosome now passes 

 undivided to one pole, thus producing two groups of spermatocytes, one 

 with and the other without the accessory chromosome. The resting 

 stage of the secondary spermatocytes seems to be very short. The 

 second pairing of the chromosomes in the second division was not 

 observed. The second division is equal and homotypic. The accessory 

 chromosome divides like the ordinary ones. The behaviour of the 

 centrosome in the development of the spermatozoa is almost the same 

 as that described by Meves for man. The chromatoid corpuscle, 

 appearing in the growth stage, seems to be cast out finally. The 

 mitochondria appear during the postsynaptic stage. In the spermatids 

 most of them give rise to a mass similar to the " Nebenkern " of 

 insects ; the main portion finally comes to occupy the middle part of 

 the spermatozoon. J. A. T. 



Spermatogenesis in Ox. — K. Masui {Journ. Coll. Agric. Imp. Univ. 

 Tokyo, 1919, 3, 377-403, 3 pis., 1 fig.). In embryos and quite young 

 animals the spermatogonia divide by amitosis. The cells seem to be 

 degenerating, being used as nutritive materials by others. The resting 

 nuclei in both the last and the penultimate spermatogonial generations 

 usually contain a large nucleolus and a small chromatin mass. The 

 number of chromosomes in the spermatogonia is thirty-three ; they 

 vary considerably in size and form, but occur in pairs. Each splits 

 longitudinally along the cleft which appeared in the spireme stage. No 

 special chromosome with different behaviour was to be seen. In the 

 telophase of the last spermatogonia the chromosomes are not fused. 

 They become lengthened into leptotene threads. Conjugation of 

 chromosomes probably takes place by telosynapsis during the synaptene 

 stage. In this stage the leptotene threads converge towards one side of 

 the nucleus, leaving a clear space on the other side. During the final 

 prophase the longitudinal splitting and transverse constriction of the 

 chromosomes are to be seen. The chromosomes are divided along the 

 constriction in the first reducing division. In the second reducing 

 division all the chromosomes become so placed that the line of the 

 longitudinal split coincides with the equatorial plane, and along this 

 line all the chromosomes (the accessory ones included) are divided at the 

 same time. Thus it is simply an equation division. In the sperma- 

 togonia and the spermatocytes the centrosome is so minute that it 

 cannot be distinguished from the other granules. Its changes during 

 the formation of spermatozoon can be followed and are seen to differ 

 considerably from those in the horse. The chromosome nucleolus or 

 the accessory chromosome can be traced throughout the growth stage 

 and the reduction division. The idiosome appears as a cytoplasmic 



