626 ROBERT H. BO WEN 



Fig. 12. — Cross-sections of the nebenkern in a condition slightly younger 

 than that of fig. 10 ; A, through the chronio|)hiIic material ; B, above 

 (or below) the ehroiuophilic material. From adjacent sections of the same 

 nebenkern. 



Fig. 14.^ — iSmall jiortion of a nebenkern showing the last remnant of 

 chromophilic material just prior to its complete dissolution. 



rL.\TE 25. 



Explanation or Figures. 



All the figures arc from Pygaeru hucephala. Figs. 28, 

 29, and 30 are from the same cyst. 



Figs. 15-41. — Progressive stages in the construction and fi.xation of the 

 acrosome. The material of the acrosomal granule is stained intensely 

 black in every case. The acrosomal vesicle can be clearly differentiated 

 in figs. 15 to 19 and fig. 21. In fig. 34 are shown cross-sections of the 

 acrosome at the stage (a})proximateh') of figs. 32 and 33. The total length 

 of the acrosome in the later stages of its elongation is ai)i)roximated as 

 nearly as conditions will permit. As a rule it could not be exactly deter- 

 mined owing to the extreme tenuity of the tip. 



Plate 26. 

 Explanation of Figures. 



All the figures are from C'allosamia promethea. 

 Fig. 44 is from the small generation of spermatids. 



Fig. 42. — Primary spermatocyte, growth period, to show the chondrio- 

 somes. 



Fig. 43. — Final telophase of the second spermatocyte division, showing 

 first step in the condensation of the nebenkern. 



Figs. 44, 46, 48, and 49. — Progressive stages in the transformation of 

 the nebenkern and the deposition of the acrosome. The acrosome (in 

 figs. 46, 48, and 40) appears as a more or less darkly-stained spherical body 

 in contact with the nuclear membrane, and closely related to adjacent 

 Golgi bodies. 



Fig. 45. — Ci'oss-section of the nebenkern in an early stage of elongation. 



Fig. 47. — Cross-sections of the nebenkern at the stage of tig. 46 : A, 

 through the region of the chromophilic material ; B, immediately above 

 or below the chromojjhilic material; (', near the much elongated, free 

 (or attached) end of the nebenkern. 



Figs. 50-60. — -Progressive stages in the formation of the definitive 

 acrosome. The length of the acrosome has been approximated as closeh 

 as possible in figs. oS and 59. In fig. 60 only a part of the acrosome is 

 shown. 



