68 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The speciiueus bad been lying in alcohol about three months. They had not been 
especially prepared for histological study, and it is ijrobable, therefore, that many 
interesting features in the finer anatomy have not been brought out iu my researches. 
All the descriptions of histological structure in this paper, as well as the sketches 
whieh are appended, are based on the carmine preparations. 
Museulature and ho dy -layers . — The layers of the anterior region of the body, where 
they are unmodified by the incipient genitalia, have the following arrangement : There 
is first a thin outer cuticular layer. This is structureless, but appears to be continuous 
within, with a series of longitudinal muscles. The latter, iu transverse sections, pre- 
sent the appearance of radial idates, attached to the outer cuticular layer (plate XXIV, 
fig. 0). The interstices between the plates of longitudinal muscles are filled with a 
granular or nuclear protoplasm which is strongly stained. Towards the inner portion 
of this gran ulo- fibrillar layer there are numerous calcareous bodies. Xext within the 
granulo-fibrillar layer is a porous or vascular layer, in which a few fine connective fibers 
and protoplasm, with abundant nuclei, can be distinguished. Tlie loose, open charac- 
ter of this layer is due to the numerous peripheral vessels of the vascular system (plate 
XXIY, fig. 6,/). Xext is a thick layer of strong, longitudinal muscles. In ti-ausverse 
sections the bundles of fibers of this layer are seen to be separated by plates of radial 
fibers, which cross from one lateral face of the body to the other, being reduced to very 
fine fibers in the peripheral regions, except in the subcuticular layer, where the plates 
of longitudinal muscles are probably derived from them. In longitudinal sections, 
parallel to the lateral faces, the radial plates appear as short connecting bands between 
the bundles of longitudinal fibers (plate XXIV, fig. 5). There are very few calcareous 
bodies and little or no granular protoplasm iu the layer of longitudinal muscles. Xext 
is a layer of coarse, strong, circular muscles or, more properly speaking, fibers running 
transversely from margin to margin, and surrounding a central space, which represents, 
in transverse sections, a central' core of the body. The layer of circular fibers is crossed, 
like the longitudinal layer, by radial fibers, which in the inner parts of the layer are 
distinct, but iu the outer portion begin to be collected into bundles, which, in turn, be- 
come the radial plates of the longitudinal layer. In the outer part of the circular layer, 
where the radial fibers are collecting into bundles, transverse sections show a reticu- 
lated structure, made by the crossing of the radial bundles and the circular fibers, 
which here also form bundles. In the meshes of the net-work thus formed are a few 
longitudinal fibers. Calcareous-bodies are sparsely scattered through this layer, while 
nuclei are somewhat abundant. The inner core is crossed by numerous parallel fibers, 
running from side to side of the body, and which are continuous with the radial fibers 
of the eircular and longitudinal layers. In the anterior part of the body these fibers 
predominate, but in the median and postero- median regions of the body they become 
much attenuated and scattered. There are also a few fine fibers transverse to these, 
i. e., running from margin to margin. The inner core, in the anterior part of the body, 
is thickly beset with calcareous bodies, and contains very numerous nuclei. 
In the above description regard is had mainly to the arrangement of layers as they 
occur in the anterior regions of the body. In sections made from portions taken from 
near the posterior end the different layers will be found to have undergone much modi- 
fication, although the general distinctive character of each remains. The radial fibers, 
or, better, those which are parallel with the smaller diameter of the elliptical cross- 
