AND OF HYBRID PIGEONS. 
59 
Wilcox, E. V: Spermatogenesis of Calloptemus femtir-rub- 
rum and Cicada tibicen.—Bull, of the Mus. of 
Comp. Zool., Harvard Coll., XXVII, i, 1895. 
ZojA, R: Sullo independenza della cromatina paterna e ma- 
terna nel nucleo delle cellule embrioli.—Anat. 
Anz. XI, 1895. 
ZuR Strassen, O : Ueber die Riesenbildung bei Ascaris-Eiern. 
—Arch. Entwm., VII, 1898. 
EXPLANATION OF PLATES I. AND II. 
a. 
axial filament. 
s. 
Sertoli or nurse cell. 
c. 
centrosome. 
scy^ 
primary spermatocyte. 
ch. 
chromatin. 
scy^ 
secondary spermatocyte 
ec. 
extra-nuclear chromatin. 
sg. 
spermatogonia. 
h. 
head. 
st. 
spermatid. 
hs. 
head-spine. 
t. 
tail. 
i. 
sphere or idiozome. 
tr. 
tetrad chromosome. 
1 
nucleolar-like linin mass. 
V. 
vacuole. 
0. 
oil-globule. 
z. 
intermediate body. 
Fig. 
1. X 550—Transverse 
section 
of a small area of a 
tubule showing all four types of germinal 
cells and also the Sertoli cell with sper¬ 
matozoa attached. The spermatogonia 
(sg) lie next the tubule wall and the sper- 
matins (st) next the lumen of the tubule. 
Fig. 2. X 550—Transverse section showing primary and 
secondary spermatocytes in process of 
division. 
Fig. 3. X 2000—A spermatogonium in the resting condition. 
Fig. 4. X 2000—A spermatogonium shortly before division 
in which a strand of nuclear material (ec) 
is being cast out into the sphere. 
Fig. 5. X 2000—A spermatogonium ready for division. 
Fig. 6. X 2000—A young primary spermatocyte. 
