LIFE HISTORY OF A TROUT PARASITE. 
347 
longitudinal, circular, and radial. Some of tlie radial fibers, however, are continuous 
[ with longitudinal fibers of the body. The first of these, the longitudinal, is fairly well 
!, developed in the larval stage, the latter two, the circular and radial, but feebly 
i; developed. Each is represented by many strong fibers in the adult. In both larva 
I and adult there is a layer of well-developed longitudinal fibers immediately beneath 
the cuticle of the bothria. (Fig 34, s c.) 
I The layers of the body have the following disposition (Fig. 27) : 
1 (1) Tlie cuticle, which appears, when highly magnified, to contain minute circular 
jj fibers. 
j (2) A thick granule -fibrous layer, the outer portion of which consists mainly of 
longitudinal fibers, which, in transverse sections, are seen to be continuous, with 
! radial sheets of connective tissue. The inner portion of this layer is less distinctly 
' fibrous and more granular. In transverse sections the connective tissue of this 
li layer appears as radial fibers, which become thicker near the cuticle, where they 
ij are more or less parallel, somewhat branched, the branches, anastomosing. Toward 
i! the inner part of the layer they lose their parallelism and form a me>h of fine fibers. 
|| This layer contains the peripheral system of vessels, which, however, is not so promi- 
I nent as it is in the larval stage. Towards the inner edge of this layer in mature and 
maturing segments the granular parenchyma is collected into roundish masses, form- 
ing the vitellaria. 
(3) A layer of coarse longitudinal muscle fibers. In the interstices between 
these fibers there are fine connective fibers which extend from the outer granulo- 
I fibrous layer, and are continuous with connective fibers of the central core, 
j (4) A thin layer of fine circular fibers surrounding a central space. 
' (5) The central core of the body. This space, where not occupied by the geni- 
; talia and the vessels of the water- vascular system, is filled by a net- work of connect- 
i ive fibers in mature segments, but in the anterior immature part of the strobile it 
j contains much granular protoplasm, from which later the genitalia develop, the tes- 
[ ticular lobules developing towards the margins, while the cirrus bulb, vas deferens, 
vagina, ovary, shell-gland, and uterus develop in the vicinity of the median line. 
The marginal canals and the aquiferous vessels, which lie in the central core, have 
practically the same characters, proportions, and disposition as they have in the larval 
form, as elucidated in my former paper. 
A few nuclear clusters, which appear in some of the transverse sections made 
near the anterior end of the head, are probably nerve ganglia (Fig. 34, n). Calca- 
reous bodies, so abundant in the larva, appear to be entirely wanting in the adult. 
GENITALIA. 
The genital apertures are close together, but distinct, lateral, about on the me- 
dian line; the male orifice much larger than the female and situated near the anterior 
edge of the segment; the female orifice is situated behind the male orifice and a little 
to one side. Sections show that the male orifice (Fig. 25) communicates directly with 
the relatively large, oval, cirrus bulb, which contains muscular fibers in a loose, open 
tissue, among which the cirrus is usually retracted. The bulb is embedded deeply in 
the segment, lying for the n ost part in the central core between the longitudinal 
muscle layers. At its base it is in connection with a sub-globular organ (Fig. 25, jt), 
which appears to be a short vas deferens, or, since its walls are rather thick and dense 
