EXPLANATION OF FIGURES. 



All figures were drawn at table height with the aid of a camera lucida. With the 

 exception of those on plate i and figs. 63-65, all figures were drawn with the use of the Zeiss 

 1.5 mm. apochromatic objective and the 12 compensating ocular; the figures on plate I were 

 drawn with the use of the Zeiss 2 mm. apochromatic objective (N.A. 1.30) and the 6 com- 

 pensating ocular and were then enlarged to 1825 diameters, while figs. 63-65 were drawn 

 with the use of the Zeiss 1.5 mm. apochromatic objective and the 8 compensating ocular. 

 In studying the cells the Zeiss 1.5 mm. apochromatic objective as well as the 2 mm. 

 (N.A. 1.40) were used in combination with the 8 compensating ocular. Figs. 8-65 were 

 drawn from sections, 5 micra thick, of material fixed in Flemming's fluid (stronger solution) 

 and stained with iron haematoxylin followed by gentian violet and erythrosin. 



Plate i. 



(Initial magnification 1825 diameters, not reduced.) 



I to 5. Three progressive stages in the development of the apyrene spermatosome, drawn 

 from living material. Figs, i and 2 show corresponding stages viewed in planes 

 at right angles to each other; figs. 3 and 4 are similar views of a later stage. 



6. Adult apyrene spermatozoon, drawn from a specimen fixed with osmic vapor and stained 



with iron haematoxylin. 



7. Adult eupyrene spermatozoon, drawn from a specimen fixed with osmic vapor and 



stained with iron haematoxylin. 



Plate 2. 



(Initial magnification 3450 diameters, reduced one-third.) 



8 to 14. Various stages in the growth of the apyrene spermatoblast from the earliest 



appearance of the centrosomal structure until a time just before it disappears and 



the nuclear membrane is dissolved. 

 15 and 16. Two consecutive sections through a single cell showing the initiation of the 



changes which occur to the nucleus and the centrosome. The mitochondria are 



shown lying around the centrosome (fig. 15). 

 17 and 18. Two consecutive sections through a single spermatoblast in the same stage as 



the preceding one. Note that the centrosome has disappeared. 

 19 and 20. Two consecutive sections through a single spermatoblast showing the scattering 



of the chromatic masses after the dissolution of the nuclear membrane. 



Plate 3. 



(Initial magnification 3450 diameters, reduced one-third.) 



21, 22, and 23. Three consecutive sections through a single spermatoblast showing the 

 appearance of groups of centrioles at the periphery of the cell. 



24 and 25. Two consecutive sections through a single spermatoblast showing the completed 

 fragmentation of the chromatic masses to form the ultimate karyomerites. 



26 and 27. Two consecutive sections through a single spermatoblast showing the appearance 

 of the centrioles on the periphery of the originally proximal half of the spermato- 

 blast and the vesiculation of the karyomerites, 



28 and 29. Two consecutive sections through a single spermatoblast, showing the grouping 

 of the centrioles and the growth of the flagella. 



30, 31, and 32. Three consecutive sections through a single spermatoblast of the same age 

 as the preceding one, showing the rays which extend from the centrioles into the 

 interior of the cell. 



Plate 4. 



(Initial magnification 3450 diameters, reduced one-third.) 



33. A section through a very young spermatosome. The centrioles have gathered at the 



base of the cell but have not yet divided. 



34. A section through a spermatosome in the stage in which the centrioles are dividing. 



35. A section through a spermatosome after the division of the centrioles showing the 



manner in which the axial fibers are formed. 



238 



