ANATOMY OF THE EARTHWORM. 1] 
ments. In structure each is a membranous bag of very 
considerable vascularity, composed of a delicate fibrous - 
tissue, and an internal secreting surface, the whole being 
distended with its contents, which are zoosperms in all 
stages of development. The fibrous tunic of each pair of 
testes, which appears to be slightly elastic, is continued 
across the median line, forming in each case a sac, which may 
be considered as a ‘ seminal vesicle,” the lobulated glandular 
bodies, in each case, being somewhat apart; the fibrous 
sheath connecting the two, and forming the delicate sac or 
bag, envelopes the expanded termination of two efferent tubes. 
This hag is extremely delicate, and easily ruptured ; though 
no very large accumulation of spermatozoa ever takes place 
in it, yet, im position, it is a seminal vesicle; the connec- 
tion between it and the lobulated testicle on either side is 
considerably constricted. The testes, then, in the earthworm, 
consist of a double pair in the eleventh segment, connected 
by their fibrous sheath with one another, and with the ex- 
panded termination of the vasa deferentia, and of a single 
larger pair in the twelfth segment similarly connected. 
The contents of the testes are very remarkable, and were 
the cause of numerous errors as to the true nature of those 
bodies. Cysts of Gregarinide (Monocystis Lumbrici), and 
free individuals of the same parasite, as also of the Anguillula 
Lumbrici, abound. The development of the zoosperms is very 
apparent; they can be traced from the form of a minute 
cell, up to the aggregations of ciliated vesicles, which 
eventually disperse (figs. 7—11, Pl. I). With regard to the 
testes or appendages of the seminal vesicles, as Dr. Hering 
considers them, it appears to me that that author has de- 
scribed a more general communication between them and the 
sac enveloping the termination of the vas deferens than exists, 
since a constriction shuts off what I believe to be the testicle 
from the seminal vesicle or sac. M. D’Udekem appears 
unfortunately to have overlooked the presence of the seminal 
vesicle altogether. 
Vasa deferentia.—These were discovered by M. D’Ude- 
kem.* They consist of a pair of ciliated tubes commu- 
nicating with the exterior in the fifteenth ring, and bifur- 
eating in the twelfth, so that each of them has a pair of 
anterior terminations. ‘These are expansions of the tube, 
excessively fragile and delicate, as also are the tubes, thickly 
ciliated, very vascular, and enveloped in the sacs or seminal 
vesicles, formed by the fibrous sheath of the testicles, a pair in 
each sac (figs. 1, 3, Pl. I; fig. 1, Pl. 41). The expanded 
* * Mem, de l’Acad. Roy. de Bruxelles,’ 1856, 
