2 ROBERT H. BOWEN 
AMPHIBIA 
Accounts of the formation of the acrosome and the middle- 
piece in the urodele sperm have long presented a most puzzling 
contradiction. According to Meves (’97), in Salamandra, the 
acrosome (‘Sphaerenblaeschen’) arises by the fusion of many 
small, clear vesicles which appear in the idiosome (‘Sphaeren- 
substanz’) of the spermatid. The vesicular acrosome thus 
formed becomes the apical body of the sperm, while the remnant 
(‘der kleine Rest’) of the sphere substance disappears completely. 
The ‘middle-piece,’ on the other hand, is formed by the proximal 
centriole alone, which penetrates the nuclear membrane and thus 
comes to lie inside the nucleus. But McGregor (’99), who has 
made a similar study of Amphiuma, gives a quite different inter- 
pretation of these details. According to McGregor, the acro- 
some arises from the sphere (idiosome) in a manner essentially 
similar to that described by Meves, except that the remnant of 
the sphere does not disintegrate. Instead it migrates with the 
centrioles to the opposite pole of the nucleus, where it forms the 
major part of the middle-piece, in which the small, spherical 
proximal centriole becomes embedded. McGregor also describes 
the penetration of the middle-piece into the nucleus, both authors 
thus agreeing that the middle-piece is intranuclear. With re- 
spect to the fate of the sphere remnant (Golgi remnant of my 
nomenclature) and the origin of the middle-piece, there was thus 
a discrepancy which has never been cleared up. It was with the 
idea of ascertaining the true relations of the Golgi apparatus 
(plus idiosome), acrosome, and centrioles that this work was 
undertaken. The material for this study has been drawn from 
a single species, Plethodon cinereus Green, though I hope eventu- 
ally to examine other urodeles in a comparative way. 
The cytoplasmic structures so far made out in the primary 
spermatocytes are of at least three categories, the Golgi appa- 
ratus-idiosome complex, the mitochondria, and a number of 
darkly stained granules of doubtful nature, but possibly to be 
considered as chromatoid bodies. The mitochondria, present 
in rather limited amount, occur as more or less scattered rodlets 
of very small diameter, similar to those figured in Geotriton by 
