624 THE AMERICAN NATURALIST. (Vor. XXXVI. 
their course in sections. It seems probable, however, that 
there is no constancy in the nature of these coils, as the num- 
ber of sections of the tubes varies greatly in different speci- 
mens. Iam reasonably certain, however, of the three attached 
and two free tubes, as the cross sections show quite uniformly 
in the anterior portion of the abdomen multiples of three, and 
in the posterior, multiples of five. The variations from this 
number can be accounted for by turns in the tubes. 
Connecting the silk receptable with the spinneret, which 
occupies the last three abdominal segments, is a tube which 
seems to have a straight course except for a bend ventrally in 
the sixth segment. This is the outlet for the silk secretion 
which collects first in the silk receptacle. The walls of this 
outlet tube have somewhat the structure of those of the Mal- 
pighian tubules, yet the cells are more regular in shape and 
have greater uniformity in the size and number of their 
nuclei. They also show, in a slight degree, the columnar 
nature of intestinal cells. This fact, together with the ventral 
bend in the course of the tube and its terminations, indicates 
that it is the small intestine, entirely diverted from its original 
function and modified so as to serve merely as an outlet for 
the silk secretion. 
After passing through this tube, the silk collects in the 
spinneret, the walls of which are surrounded by bands of strong 
circular muscles, which aid in ejecting the secretion when the 
cocoon is spun. 
In Fig. 10 the nature and position of the spinning glands 
are shown diagrammatically. The complete course of one of 
the three which are attached at both ends, and of one of the 
two which are attached at one end, is figured. 
Fig. 11 shows longitudinal and cross sections of the silk 
glands with their fantastically formed nuclei. The typical 
structure of the Malpighian tubule is also shown and its grad- 
ual modification into silk-secreting cells. In a, Fig. 11, 4 
section of a functional silk gland is shown, the walls being much 
thinner and the nuclei of simpler forms than in å of the same 
figure, where no secretion is visible. Some of the sections 
figured show traces of vacuolization, a common sign of the 
