The Spermatogenesis of the Opossum (Didelphys virginiana) etc. 
73 
kangaroo (von Korff, 1902), macaque (Moreaux, 1909) and man 
(Benda, 1897; Meves, 1899). Moreaux (1909) snmmarizes very briefly 
the facts respecting the histogenesis of primate spermatozoa. A good 
historical review of the literature relating to the histogenesis of the mam- 
malian spermatozoa will be found in Hertwig’s Handbuch and in the 
works of Regaud (1908), Retzius (1909), Duesberg (1910), and Leplat 
(1910). 
Discussion. Study of living spermatozoa and of stained smear 
preparations from the vas deferens of the Opossum shows that the “mature” 
Spermatozoon of the seminiferous tubules undergoes still further changes 
in passing througli the epididymis to the vas deferens. In the testes 
the body and spiral filament are coextensive with the middle-piece. In 
the sperm of the epididymis the “body” covers only about one half 
(subsequently still less) of the middle-piece, and lias opened up ventrallv, 
thus forming a sort of bilateral fin for the middle-piece, anteriorly United 
to the limbs of the U-shaped head. Moreover, a delicate spiral thread 
appears in the upper end of the flagellum apparently continuous with 
the spiral filament of the middle-piece. Also, the middle-piece is now 
slightly narrower than the flagellum at the point of union (a conspicuous 
plate) and the limbs of the U-shaped head are now flattened and curved 
slightly downward and outward (text fig. 2). In the globus minor, the 
sperm arc still unpaired; in the vas the vast majoritv are paired and 
swim very actively. After several minutes on the slide manv pairs 
disjoin (apparently by violent traction. thus producing torn surfaces) 
and move about very rapidly independently. In the light of tliis last 
Observation it appears probable that the temporarilv paired (a very 
intimate lateral fusiou, apparently involving cytoplasmic continuity) 
spermatozoa again separate prior to fecundation. 
The middle-piece of the Spermatozoon of the kangaroo is derived, 
according to von Korff (1902) from mitochondrial elements. The latter, 
however, do not apparently form a spiral filament. 
Duesberg (1908) described the formation of the spiral filament of 
the rat by a confluence of granulär mitochondria progressing from the 
head caudally. In his later paper Duesberg derives the spiral filament 
by a deposit among the mitochondria of a liomogeneous substance which 
stains like mitochondria. The Aebenkern (i. e. the hyaline sphere) accord- 
ing to Regaud, Retzius and Duesberg becomes the acrosome; and the 
idiozome, or idiozome remnant, disappears. The cytoplasm of the spermatid 
does not here contribute to the middle-piece. This, according to Dues- 
berg, is formed solely from the ring centrosome and all the mitochondria. 
