THE SPERMATOGENESIS OF DOMESTIC MAMMALS. 401 
IV. The ‘accessory’ chromosome in Syromastes and Pyrrhocoris, with comparative review 
of the types of sexual (differences of the chromosome-groups. 1bil. Vol. VI. 
——_——,, (1912): Studies on chromos>mes, 
VIII. Observation on the maturation-phenomena in certain Hemiptera and other forms, with 
“ considerations on synapsis and reduction. Ibid. Vol, XIII. 
‚ (1913): Achromatoid body simulating an accessory chromosome in Pen‘atoma. Biol. 
Bull. Vol. XXIV. 
WODSEDALER, J. E., (1913): Spermatogenesis of the pig with special reference to the accessory 
chromosomes. Biol. Bull. Vol. XXV. 
, (1914): Spermatogenesis of the horse with special reference to the accessory chromo- 
some and chromatoid body. Ibid Vol. XXVIL 
Yocom, B., (1917): Some phases of spermatogenesis in the mouse. Am. Calif, Publ. 
° 
EXPLANATION OF PLATES. 
The figures were drawn with the aid of acamera lucida, Figs, 22—29, 34—38 and 46—98 were 
drawn with a Zeiss 1/12 objective and compensating ocular 12, Figs. 3—21, 30—33 and 39— 
45 with a Zeiss 1/12 objective and a Zeiss 4 ocular, Figs. 1, 2 with a Zeiss D objective and a 
Zeiss 4 ocular, 
PLATE XLY, 
Fig. 1. Section of testis of an embryo, showing differentiation of spermatogonia, 
Fig. 2. Section of testis of a quite young animal, showing spermatogonium and amitotie 
division, 
Fig. 3. Section of testis of a quite young animal. 
Fig, 4. Spermatogonium in the earliest generation. 
Fig. 5. Spermatogonium ; the nucleoli break into small pieces, 
Fig. 6. Spermatogonium which contains two nucleoli. 
Fig. 7. Sperma‘ogonium showing division of nucleoli. 
Figs. 8, 9. Early stage of amitotic division, showing irregular outline of nuclei. 
Fig. 10. Amitotic division of a apermatogonium, showing fission of nuclear wall and a sphere. 
Figs. 11, 12. Amitotic division. 
Figs. 13—17. Multinuclear cells produced by amitosis. 
Figs. 16, 18. Amitotie division, showing chromatin spiremes. 
Fig. 19, Resting spermatogonium in the earliest generation. 
Figs. 20, 21. Spireme stage of spermatogonia in the earliest generation. 
Figs, 22, 23, Prophase nuclei of spermatogonia in the earlist generation. 
) Fig. 21. Prophase nucleus of a spermatogonium in the earliest generation, showing 
longitudinal split of chromosome. 
Fig. 25. Nucleus of a spermutogonium (the earliest generation) in the late prophase. 
