DESCRIPTION OF PLATE. 



Fixation: Flemniing's strong solution. Stain: Heidenhain's iron haematoxylin. 

 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 a-xial filament and middle 

 piece. 



18 and 19. Formation of spiral filament by coales- 

 cence of mitochondria. 



20 and 21. Ftice 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 stage" 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 primary 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). 



