FISH ENTOZOA FROM YELLOWSTONE PARK. 5A9 
larger specimens is rather sharply marked off from the body for a dis- 
tance of 8 mm. or more. The anterior end is somewhat lighter colored 
than the body and suggests the head of some species of Dibothrium, 
but there are no bothria. The body, especially toward the posterior 
end, is yellowish-white. 
ANATOMY. 
The sections upon which the following account of the anatomy is 
based were made from specimens stained in toto in borax earmine. 
Structure of the head.—Upon examining transverse and longitudinal 
sections of the head it is seen to consist of somewhat spongy tissue, in 
which there are a few longitudinal muscular and connective fibers and 
numerous protoplasmic granules and granular masses contained in a 
mesh of transverse connective fibers. There are also numerous small 
open spaces shown in the sections which are doubtless the fine and 
irregular branchings of the vessels of the water-vascular system. 
Figs. 9 and 10 show the structure of the head of a small specimen. In 
them it is seen that the cuticular layer is very thin and the subeutie- 
war. granulo-fibrous layer, which is clearly defined toward the middle 
of the body, is but faintly foreshadowed. The longitudinal muscular 
fibers are not collected into any definite area, but are distributed 
pretty uniformly among the other tissues. There is no indication of 
layers of any kind. If the entire section, from which Fig. 10 was 
sketched, had been figured it would have shown no peculiarities of 
structure that are not shown in the small portion which is represented. 
No calcareous bodies were found in any of the sections. One of the 
smallest specimens was placed in hydrochloric acid, but no evidence of 
the presence of caleareous particles was educed. 
Structure of the body.—There is arather abrupt transition between 
the head and the body. When transverse sections made through the 
anterior part of the body immediately back of the head are compared 
with those, of the head several differences may be observed. The - 
cuticle is thicker and more sharply defined. In the center of the 
section the connective fibers assume a parallelism, especially in a 
direction from margin to margin, which is in marked contrast with 
the irregular course which they pursue in the head. The open spaces, 
which indicate the situation of longitudinal vessels, are collected 
towards the periphery. The protoplasmic granules in the center soon 
begin to collect into clusters, which represent the beginnings of the 
testes. 
In a small specimen about 5 mm. long, which was cut into transverse 
sections, if was not until the middle, or a little back of the middle, 
counting from the head, that the longitudinal muscles began to collect 
into bundles to form a somewhat discontinuous layer surrounding the 
inner space. 
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