DESCRIPTION OF PLATE. 



Fixation: Flemming's strong solution. Stain: Heidenhain's iron hasmatoxylin. 

 Magnification: 1500 diameters. 



Mongoose. 



1. Spermatogonium; the nucleus contains three 



small plasmosomes. 



2. Spermatogonium; the nucleus is in process of 



amitotic division. 



3. Primary spermatocyte; the nucleus contains a 



centrally located plasmosome; the delicate 

 chromatic reticulum consists of an apparently 

 continuous single thread; leptotene-nucleus. 



4. Bouquet stage; the slightly thickened spireme has 



aggregated in a close-meshed mass at the 

 idiosome pole of the nucleus; the cytoplasm 

 surrounding the idiosome contains pale mito- 

 chondria; synizesis, polarized amphitene. 



5. Synapsis: the disentangling threads are pairing 



side by side; the nucleus is still approximately 

 of the same size as in the resting spermatocyte, 

 hence synizesis and synapsis signify activity 

 (motion) on the part of the nuclear reticulum; 

 synaptene-nucleus. 



6. Postsynapsis; early prophase; diplotene-nucleus. 

 7 and 8. Later prophases; at no stage do hetero- 



chromosomes appear. 

 9 and 10. Side and polar views respectively of 

 metaphase plates; no chromosome is conspic- 

 uous for unusual size or behavior; the number 

 of chromosomes is approximately twenty- 

 four, the haploid group. 



II. Resting secondary spermatocyte. 



12 and 13. Side and polar views respectively of 

 metaphase plates; the number of chromosomes 

 is approximately twelve, forming a hemioid 

 group. 



14. Spermatid; the cytoplasm has become filled with 



pale mitochondria. 



15. Appearance of "sphere" and centrosome. 



16 and 17. Appearance of axial filament and middle 

 piece. 



18 and 19. Formation of spiral filament by coales- 

 cence of mitochondria. 



20 and 21. Face and profile views respectively of 

 mature, living spermatozoa. 



White Mouse. 



22. Spermatogonium. 



23. Primary spermatocyte, nucleus at leptotene 



phase; the bilobed nucleolus may be a pair of 

 heterochromosomes. 



24. Synapsis, polarized amphitene, bouquet or 



synaptene phase; the heterochromosome is 

 apparently single. 



25. Postsynapsis; early prophase; heterochrome (or 



accessory) conspicuous; pachytene-nucleus. 

 26 and 27a. Early and late prophase groups respec- 

 tively, both including conspicuously the pair of 

 heterochromosomes almost invariably situated 

 on the nuclear wall and close to the idiosome; 

 26, diplotene-nucleus. 



276. Metaphase; one of the chromosomes has moved 

 in advance of the others to one pole; this has a 

 tetrad form and is still clearly bivalent; ac- 

 cordingly, it fails to divide in this mitosis and 

 may represent the "accessory" of the growth 

 stages. 



Sheep. 



28. Resting primary spermatocyte, showing the 



accessory at the idiosome pole; perhaps post- 

 synaptic "confused sta;j;e" of Wilson. 



29. Bouquet (synapsis) stage; the accessory chromo- 



some is attached to a double thread, and in- 

 variably lies close to the nuclear wall. 



30. Postsynapsis; early prophase, showing a bipartite 



accessory (or pair of heterochromosomes) . 



Horse. 



31. Primary spermatocyte; the nucleus contains 



two irregular karyosomes and a bilobed 

 chromatic nucleolus, probably a pair of hetero- 

 chromosomes. 



32. Synapsis stage, showing the heterochromosomes 



among the pairing threads close to the nuclear 

 wall. 



33. Postsynapsis, showing a tripartite X-element, 



the heterochromosome group; pachytene- 

 nucleus. 



Mule. 



34. Resting prima:y spermatocyte, showing a 



divided, or paired, heterochromosome. 



35. Synapsis stage, showing a heterochromosome. 



36 and 37. Early and late prophase stages respec- 

 tively, showing a pair of heterochromosomes. 



Bull. 



38. Postsynapsis, showing an accessory chromosome 

 among the bivalent threads, close to wall and 

 idiosome; diplotene-nucleus. 



Dog. 



30. Primary spermatocyte; presynaptic resting 

 phase, showing plasmosome and bilobed 

 monosome. 



40. Postsynaptic phase, pachytene-nucleus; mono- 



some attached to one of the threads. 



41. Early prophase, diplotene-nucleus; chromosomes 



in form of long bivalent threads; monosome 

 close to nuclear wall. 



42. Oocyte from ovary of 23-day cat. Synapsis. 



True nucleolus; monosome divided longitu- 

 dinally (after H. von Winiwarter et G. Sain- 

 mont, fig. 43). 



