198 THE MICROSCOPE. 
in the body wall the following clearly marked layers as shown in 
Fig. 1. Cu, is a thin, structureless cuticle. Itis thin and, under 
certain conditions, it separates readily from the subjacent tissues. It 
is marked with fine parallel striz, which give the irridiscence pecu- 
liar to thin films. It is perforated by many pores, through which 
are discharged the products of gland cells lying in the next layer, 
ep. This consists of columnar cells, many of which are enlarged to 
an oval form by the accumulation of mucus or other products. The 
layer c m, is muscular, the fibres running in a circular direction. 
The investigation of these fibres is not, as yet, satisfactory, and no 
account of them has come to notice. They are much elongated, and 
a very small oval nucleus can sometimes be detected. At 1 m, 
appear the longitudinal bands of muscles. Their peculiar appear- 
ance is due to the arrangement of the bundles of fibres. On each 
side of a flat plate are arranged the lateral ridges which in section 
appear as delineated. In longitudinal section the circular muscles 
show the same structure, but in a less marked degree. Within the 
muscular layers is the thin layer p e, of peritoneal epithelium. This 
is reflected, and also covers the alimentary canal. It is extremely 
difficult to make out, and is doubtfully visible in cross sections. By 
means of other preparations it becomes evident that the tissue con- 
sists of flattened pavement cells united at their edges, and having 
a vascular net-work just beneath. It will be readily seen from the 
figure that the wall is marked off into eight regions, with limits shown 
by the setze. Upon the back, the color is darker than at the side or 
beneath. This is found to be due to masses of pigment disposed 
among the fibres of the circular muscular layer. 
The cavity marked co, in this figure, is known as the cwlomic 
cavity. It is divided by cross partitions extending from the body 
wall to the intestine into a series of ring-like spaces which corres- 
pond to the external segmentation of the body. In this cavity there 
circulates during life a fluid which has histological features worthy 
of notice. This ccelomic fluid is nearly colorless, or with a slight 
milky tinge, and in it float amceboid cells. The fluid is likely also to 
harbor a considerable number of parasitic protozoa, especially the 
elongated gregarines. These may be obtained by drawing the worm 
through the fingers, forcing the fluid into one end. If then the 
swollen extremity be punctured with the point of the scalpel and 
the issuing drop received upon a slide, it affords means for a very 
interesting study. 
In the center of the figure is the alimentary canal. At d v, 
is the dorsal blood vessel which runs the whole length of the worm 
