The Spermatogenesis of the Opossum (Didelphys virginiana) etc. 
71 
the acrosome) after the middle-piece is formed; and the idiozome seems 
to fragment and disappear within the body about the same time. It is 
possible that both of these structures may contribute something to the 
middle-piece, more particularly the ]\ T ebenkern, but the evidence is in- 
Text Figure 1. 
Text Figure 2. 
Text Figure 1. Illustration showing tbe latest stage of development attained by the spermatozoa in 
tlie testis. Kemnant of Nebenkern (homologue of acrosome?) still visible. Xl'OO. 
Text Figure 2. Camera lucida drawing (ventral viewi of Spermatozoon from smear preparation (stained 
with carbol-fuchsim from vas deferens, showing head, middle-piece, flagellum and end-piece. X 1500. 
decisive. The middle-piece is cigar-shaped, the pointed end anteriorly, 
and ending in an end-knob (centrosome), the blunt end corresponding 
with the caudal limit of the body. The middle-piece contains a spiral 
filament peripherally, clearly formed of mitocliondria. The history of 
