160 ‘ REPORT—1858. | 
tions. I think this is an optical illusion, and that the appearance is due to 
the interior being furnished with numerous cavities or hollows (Plate XVI. 
fig. 104, and fig. 12). 
In Ciniflo atrox and C. ferox, and probably in the other species of the same 
family, there are a number of very minute sacs, imbedded in granular opake 
matter, which are not more than a fourth of the size of those which I have 
before described ; they are of a round or pear-like shape, with the appearance 
of a nucleus in the interior, and are furnished with exceedingly minute ducts, 
I found them close to the spinarets, beneath the skin, and their ducts pro- 
bably proceed to the minute orifices on the extremity of the extra pair of 
spinnerets ; but owing to their extreme delicacy, I could not succeed in tracing 
them there (Plate XVI. fig. 13). 
In the middle and even upper parts of the abdomen are a number of tubular 
or bag-shaped cavities, which vary much in shape, number, size, and structure 
in different species; some are hard and cartilaginous in consistence, with 
transparent walls; these present no appearance of fibres under the micro- 
scope, but when forcibly compressed, crack and break into irregular frag- 
ments. Their ducts seem similar in structure to the body of the sae, being 
hard and brittle. In Epéira diadema and Ep. quadrata these glands are of 
a large size; in the former species there are six of them, three being on each 
side; they are somewhat cylindrical in shape, and very much convoluted 
(see Plate XVII. fig.1@). I succeeded in tracing one of their ducts into each 
of the six ordinary spinnerets. In Agelena labyrinthica they are represented 
by several oval-shaped sacs, of moderate size (see Plate XVII. fig. 1 e), quite 
transparent, and so firm in consistence, that they feel like solid bodies when 
taken between the fingers. 
We now come to a series of membranous sacs, of various shapes and sizes, 
some being large and vermiform, others club-shaped, while others are dilated 
in the middle and furnished with branched ceca. All these different forms 
do not occur in the same individual, but some in one species and some in 
another; they all appear, however, to resemble each other more or less in 
structure. When any of the larger varieties are minutely examined, their 
walls appear thickened and fibrous. Their inner surface is studded with mi- 
nute cavities or hollows, giving it somewhat the appearance of the interior ofa 
piece of human intestine, with its valvule conniventes ; thus affording an in- 
creased surface for secretion. When carefully removed from the surround- 
ing textures, they all appear coated externally by soft granular matter. I 
think it probable that the blood or nutritive fluid which supplies the mate- 
rials for secretion circulates in this coat, which must therefore be considered 
as the cortical part of the gland. These sacs are well seen in Agelena laby- 
rinthica, where they are met with of a large tubular or clavate shape. I 
have figured three ( Plate XVII. fig. 7), the ducts of which I found terminating 
in one of the elongated posterior spinners; fully confirming Mr. Blackwall’s 
opinion as to the true nature of these anal palpi, as they have been called. 
In Ciniflo ferox I noticed two large branched sacs of a very peculiar form 
(see Plate XVII. fig. 6). 
One of the most interesting parts of the structure of these membranous 
sacs is the formation of their excretory ducts. A transparent and highly 
extensible tube is encircled by a fibrous or muscular coat, which loosely sur- 
rounds it, and seems to be a continuation of the outer coat of the sac itself. 
When the ducts are stretched, which they unavoidably are in their removal 
from the body, this breaks up into circular rings and becomes loose from the 
tube within, which is exceedingly extensible, and stretches out so as to be- 
come much less in diameter than the outer coat. This structure may be very 
