660 THE GENERATIVE ORGANS. 
1, DESCRIPTIVE ANATOMY OF THE INTERNAL GENERATIVE 
ORGANS OF THE MALE BLOW-FLY. 
The internal generative organs of the male Blow-fly are 
(1) a single pair of testes and their vasa efferentia ; (2) the para- 
gonia, usually termed vesicule seminales ; (3) the vas deferens ; 
(4) the ejaculatory sac; and (5) the ejaculatory duct. 
These parts are found very generally in male insects, but those 
in which the penis is absent have usually no ejaculatory sac or 
duct, and the vas deferens opens on the surface between a pair 
of more or less complex genital appendages. In some larve, 
Ephemeridz (Palmen), the external openings are paired, so that 
the vasa efferentia (segmental ducts) open directly on the 
surface. 
The Testes are a pair of simple follicles, situated one on either 
side of the median line in the dorsal part of the fourth segment 
of the abdomen. They are pyriform, and often exhibit an 
hour-glass constriction between the fundus and duct of the 
gland. They are ofa pale orange colour externally, due to the 
pigmented epithelium which forms the wall of the follicle. In 
the adult insect the testes consist of an epithelial capsule filled 
with semen. It measures *75 mm. to ‘8mm. in its long dia- 
meter, and ‘5 mm. in its transverse diameter. ‘The cells of the 
capsule are so thin that they are readily mistaken in sections 
for a cuticular layer; but in surface views their outlines are 
very distinct. In fresh preparations the capsule is readily torn 
into fragments by moving the cover-glass, when if any cuticular 
layer existed it could not fail to be apparent. 
These cells are hexagonal, they have an average diameter of 
‘o2 mm., and are pigmented with orange-brown granular pig- 
ment—they have large oval nuclei. 
Externally to the epithelium just described, the testis is 
covered by a thick layer of small, usually multi-nucleated fat- 
cells, precisely similar to those which separate the ovary from 
the abdominal wall in the female insect. Each nucleus in 
these cells is surrounded by a stellate protoplasmic mass, the 
