THE ANATOMY OF AMPHIPTYCHES URNA. 141 
muscle fibres, which is followed by a second layer of circular fibres, enclosing the 
central part of the body. This central part is occupied by the various organs—the 
reproductive, nervous, and excretory; it is crossed by dorso-ventral muscle fibres. In 
front of the reproductive organs, which traverse some three-quarters of the length 
of the body, the central part (Pl. 13, Fig. 3) is occupied by a very compact and 
homogeneous mass of connective-tissue, in which nuclei are scattered irregularly, and 
in which the excretory vessels ramify. Except the cavities of the excretory and 
reproductive organs no trace of any spaces are to be seen. In the region of the 
uterus the latter occupies by far the larger portion of the body. 
(2.) Nervous System.—This consists of a pair of longitudinal cords, strongly 
developed, and passing one along each side of the body, from the anterior to the 
posterior end. (Pl. 11, Fig. 1.) From these cords branches arise on either side, 
supplying the different parts of the body. As described by Wagener, there is also 
a stout band of fibres passing across the inner end of the sucker, and uniting the 
nerve cord of either side ventrally ; beyond this commissure, two branches pass on 
which hug the sides of the sucker, and pass to the very posterior end of the body 
(anterior of Wagener), but in this position no nerve ring is formed, so far as I can 
discover by means of sections. In the fieure the cords are represented for the sake of 
clearness, aS running one on either side of the uterus. Really they run somewhat 
nearer to the median line than is represented in the figure, and lie dorsal of the 
uterus. At the very anterior end the cords form a ring, which runs round the 
“proboscis.” The commissure on the ventral side is more strongly developed than 
that on the dorsal side, which can only be traced by means of series of consecutive 
sections. 
No nerve cells can be detected with certainty. In certain parts nuclei can be 
seen on the outer surface of the cords, but these probably belong to the connective 
tissue surrounding the cords. 
(3.) Excretory Organs.—These consist, as described in the main by Wagener, of 
a network of tubes, some of which contain cilia. This network is best developed at 
the sides and two ends of the body. The tubes all lie within the inner layer of 
circular muscle fibres. Branch vessels pass across the uterus, connecting the networks 
of the two sides, and along each side a main lateral vessel, running very irregularly 
and connected with numerous branches, can be more or less clearly distinguished. . 
(Pl. 18, Fig. 1, ne.) The vessels vary greatly in size, and cilia are confined to the 
larger ones. In these, as described by Wagener, they do not line the whole surface. 
Transverse sections (Pl. 12, Fig. 8) show clearly the structure of the vessels. Hach 
is lined by a clearly outlined membrane-like layer, which, in appearance, more 
resembles a fine cuticular structure than anything else. From one side a tuft of cilia 
projects into the lumen, having just the appearance represented in the drawing. 
