662 THE GENERATIVE ORGANS. 
The testes of many insects consist of several or numerous 
follicles, which either open separately into the vas efferens or 
unite to form a common cavity ; sometimes, as in the Lepi- 
doptera, the two testes are fused into a single median organ, 
but there are always two ducts, which often have transverse 
inter-communications. 
The Duct of the Testis, Vas Efferens—It is convenient to dis- 
tinguish the paired and azygos ducts of the testes by distinct 
names; authors usually term both ‘vasa deferentia,’ I have 
preferred to use the term ‘vas efferens’ for the duct of the 
testis, and ‘vas deferens’ for the azygos duct—formed by the 
union of the ducts of the testes and of the so-called vesiculz 
seminales, or paragonia. 
In the Blow-fly the vas efferens is a thick walled tube about 
o’7mm. in length. It hasanexternal diameter of ‘05 mm., but 
its lumen is less than half this diameter; its walls consist of 
small columnar cells; the outer surface is covered by a thin 
peritoneal layer continuous with the adipose tissue which 
covers the capsule of the testis. 
The Paragonia (Fig. 90, pg), the so-called vesicule semi- 
nales of authors, are a pair of large sacs 1°5 mm. in length and 
*3 mm. in diameter, which open with the vasa efferentia into 
the vas deferens. The wall of the sac consists of a single layer 
of long columnar cells covered externally by a thin layer of 
peritoneal tissue. The sac is filled with a granular, highly 
coagulable milky fluid. 
The paragonia of many insects are much convoluted, and in 
others exhibit numerous follicles. The term vesiculz semi- 
nales is certainly misleading, as they never, so far as I know, 
contain any seminal filaments. The Cockroach, Periplaneta, is 
an apparent exception, but I think that the real paragonia in 
this insect never contain seminal filaments. 
The relation of the Paragonia and Testes.—It is well known 
that in Periplaneta the vas deferens is short and wide and 
terminates in front in a large number of cecal gland tubules, 
which constitute the so-called mushroom-like gland of Huxley. 
These sacculi are of two kinds, and have been distinguished as 
