74 
BULLET] N OF TITE UNITED STATES FISH COMMISSION 
Fine longitudinal and circular contractile fibers were distinctly visible, (plate XXVII, 
fig. 5.) 
Longitudinal sections of the posterior end reveal a number of rudely circular open 
spaces lying in the vascular layer. Some of them are lined with a layer of fibrous 
tissue in which are numerous nuclei. Others are without any proper lining. The sec- 
tions were made parallel with the lateral faces of the specimen. Approaching from 
one end of the series the sections contain from two to four of these cavities lying near 
the extreme tip of the posterior end and giving rise to an open, porous structure. The 
longitudinal vessels appear to connect with them, as do also the vessels of the periph- 
eral layer, of which they appear to be enlargements. In sections approaching from 
the opposite direction there were two elliptical spaces, the long axes of which are par- 
allel with the long axis of the body. One of these is shown highly magnified in plate 
XXVI, fig. 5. These lay side by side and each appeared in about eleven of the sec- 
tions. The thickness of the sections was about .015 millimeter. They were completely 
inclosed in the tissues of the body except at the posterior ends where each communi- 
cates with the exterior by a short passage with nuclear walls. When the sections are 
studied with a view to reconstructing the cavities the latter are seen to be ellipsoidal, 
or more properly, lenticular. These spaces have a special lining of columnar epithe- 
lium resting on a nuclear layer and surrounded by a muscular layer which is made up 
of the continuation of the inner layer of longitudinal muscles. The latter layer also 
contains numerous nuclei. The maximum length of these spaces is .28 millimeter, 
the breadth .20 millimeter, and the thickness (estimated) .02 millimeter. They are 
filled with loose, granular tissue and delicate connective fibers somewhat like the tissue 
which fills the marginal canals, but differing from that in that the granular material 
takes a good stain with carmine. There were about fifty sections made through the 
posterior end of the specimen. The sections of these two oval vessels did not begin nor 
end at the same place in the series, although in a number they occur side by side. One 
occupies about seventeen sections; in about half of these it is accompanied by the other. 
A third vessel with the same structure, viz, thick walls of columnar tissue appears 
in a few of the seetions near the lateral face opposite the one near which the two above- 
described vessels lie. It occupies about six sections, is much smaller than the others, 
and the walls, instead of being smooth, are much folded. 
I interpret these vessels as the terminal pulsatile vessels. I was not able, from the 
single series of sections prepared for this preliminary report, to determine their exact 
relations to either the aquiferous vessels or the marginal canals. 
Calcareous bodies . — These are not abundant in the exti erne anterior end of the body, 
but soon become very abundant as one itroceeds posteriorly from the head. As in i. 
catostomi they are confined mainly to the peripheral granule- vascular layer and to the 
central core. In the latter they are very abundant. They are somewhat larger and 
present rather more irregularity in shape than do those of L. catostomi, and finer 
exami^les of concentric structure occur. The dimensions of one of the larger bodies 
were .011 millimeter and .019 millimeter in the two diameters. They are seen to be still 
abundant, particularly in the central core, in sections made through the posterior end. 
Beproductive organs . — The reproductive organs are but slightly developed. The 
beginnings of the cirrus j^ouch and the vagina are indicated by a series of clusters of 
nuclei which lie along the middle line near one of the lateral faces. Xo other traces of 
genitalia were observed. 
