SPERMATOGENESIS OF SQUILLA ORATORIA Sl. 
convoluted tubes, paired for the greater part of their length, 
only parts at the anterior extremity of the accessory gland and 
the posterior end of the gonad proper being unpaired. Start- 
ing from these unpaired parts, both the accessory gland and the 
gonad proper proceed in striking meandering courses, but largely 
along the longitudinal axis of the body, the former from anterior, 
while the latter from posterior, toward the last thoracic somite. 
At this somite, they both enter the penis, which is attached to 
the basal segment of the ambulatory leg. Somewhat before 
reaching the somite, the gonadial tube shows extreme convolu- 
tions, forming several complete loops in its course and presents 
an appearance of an entangled thread. Mature or nearly 
mature spermatozoa alone are contained in this part of the tube; 
it is consequently to be called vas deferens to distinguish it from 
the more posterior and less convoluted part, the testis in the 
strict sense. The accessory gland apparently has nothing to do 
with the production of spermatozoa; it contains neither mature 
spermatozoa nor any developmental stages of them. 
ARRANGEMENT OF SEMINAL ELEMENTS IN TESTICULAR TUBE 
As is shown in figure 1, the testicular tube is nearly round in 
cross-section and contains seminal cells representing various 
stages of development, save the central region where some 
vacant spaces are generally found. The cells are arranged in 
two or three distinct zones. In figure 1 three such zones are very 
clearly distinguishable: the outermost, made up of spermato- 
cytes in synizesis stage dispersed with some spermatogonial and 
nutritive cells, another containing young spermatids, and still 
another with advanced spermatids. A similar arrangement 
exists throughout the whole length of the tube. It may be 
noticed that the nearer the anterior end, the older the cells are. 
In a region of the outermost zone in the section of the tes- 
ticular tube, perhaps along the middorsal line of the latter, is a 
cluster of cells (fig. 1, pr.) distinguishable from the neighboring 
parts by its characteristic appearance. It consists of a few 
large spermatogonial cells (p.spg) together with some nutritive 
cells (nt) and bulges out into the mass of seminal cells of more 
