392 
Tetrm'liynchus erinaceus 
relation to the truly central elements; and (3) in the curious lack of 
definite boundaries to all these parts, with the possible exception of the 
anterior ganglia. It is indeed difficult to be sure of the distinct 
existence of a definite brain sbeath when one fails to delimit it in sections 
stained so as to bring the parenchymatous matrix into prominence. 
I think that the ganglionic region on the course of the lateral nerve 
cords has possibly been seen by Laczkb (1880). In a paper which is 
apparently only a preliminary communication this author describes 
“ machtige ” ganglionic regions in the nervous system of Tetrarhynchid 
larvae. Some of these appear to be columnar and to be situated in the 
neighbourhood of the lateral nerve cords. In the absence of figures it 
is indeed impossible to be certain as to the precise situation of these 
structures but it is possible that they are those which I have mentioned 
as giving origin to the proboscidial nerves. 
V. The integument. 
The membrane covering the outer surface of the body of a Cestode 
differs notably from that present in most other invertebrates. In such 
a form as that now being described the tissue elements are : (1) the 
cuticula; (2) the underlying parenchyma; (3) the subcuticular cells; 
and (4) the integumentary muscles. A “basement membrane” lying 
just beneath the cuticle is also frequently described, and the integument 
also contains gland cells, calcareous corpiiscles, myoblasts, nervous 
elements, and the terminal flame-cells of the excretory organs. I am 
unable in the meantime to give a detailed description of the latter 
structures. 
The cuticula. This layer covers every part of the surface of the 
body and is directly continuous at the genital aperture with the internal 
wall of the genital ducts ; and it is also continuous with the cuticular 
wall of the proboscides, and with that of the proboscis sheaths. It is 
a firm, uniform, structureless layer of variable thickness but never more 
than about O'Ol mm. in depth. It is said to be perforated by delicate 
canals running at right angles to its surface but I have been unable to 
see these. Normally it is finely granular in appearance and stains 
a light blue with methyl-blue-eosin. In sections which have been fixed 
with Zenker’s fixative there is no appearance of lamination, nor of the 
deposition of the cuticle in any definite order; but in sections fixed in 
vom Rath’s fluid and stained with iron haematoxylin I have observed 
a vertical striation. This is figured very accurately by Pintner (1880, 
