SOME LITTORAL OLIGOCHAITA OF THE CLYDE. 53 
epithelial lining (Pl. IJ. fig. 11). The ampulla communicates as usual with the ceso- 
phagus; in the living specimen it appears somewhat irregularly spherical, with projecting 
bosses. In sections the cavity is irregular in shape, possessing a few small saccular 
diverticula ; the cells composing the wall are comparatively few, large in size, irregular in 
shape and arrangement, and do not form a regular epithelial layer. The spermatozoa 
penetrate between the cells, and the appearances in sections seem to show that they burrow 
into the cells themselves ; they also seem to penetrate the wall, and are found lying on 
the outer surface (Pl. IT. fig. 11). The ampulla possesses no muscular covering. The 
duct leads obliquely forwards to the exterior; it is a little longer than the ampulla, and, 
like the latter, appears in the living condition to be studded with small rounded projections, 
smaller, however, than those of the ampulla ; round the external aperture these projecting 
cells are again larger, and form a distinct rosette of glands. The statements as to 
irregularity of shape and disposition of the cells, and absence of a definite epithelium, 
already made for the ampulla, hold also for the duct ; so that, except near the external 
aperture, it is difficult to follow the lumen in sections. The cuticle of the surface is 
invaginated for some little distance at the external aperture, and muscular fibres con- 
tinuous with those of the body-wall are conspicuous among the cells of the duct; but 
these latter are not continued on to the ampulla. 
The clatellar cells are entirely wanting over the mid-ventral region of the body, 
along an area whose breadth is the distance between the male apertures of the two 
sides (PI. II. fig. 10). 
The species to which the present form shows most resemblance, at least externally, 
seems undoubtedly to be Enchytreus argenteus, MICHAELSEN (11). The same opaque 
white colour characterises both, and in both is due to the same cause—the presence of 
opaque granular coelomic corpuscles; further, owing to the varying aggregations of these 
corpuscles in different parts of the body, the whiteness is not uniform in either. 
But, apart from such indifferent features as the colourless blood and the absence of 
peptonephridia in both (probably, since MicHar.sen does not mention these structures), 
the resemblances seem to end here. The differences in size (H. argenteus, 2°5-5 mm., 
present form 8 mm.), in number of segments (#. a. twenty-three to thirty, present form 
thirty-two to thirty-nine), and in number of setze per bundle (Z. a. two or three, present 
form regularly two), are not very great; the chief differences are those of the cerebral 
ganglion, nephridia, seminal funnel, and spermathece. 
The cerebral ganglion has a rounded posterior end in 4. argenteus, while in the 
present form it is indented posteriorly ; the seminal funnel is short, somewhat longer 
than broad in the former, while it is four times as long as broad in the latter. The 
ampulla of the spermatheca is of an inverted pear-shape in the former, and the duct 
is simple (without gland-cells) ; the peculiarities of these structures in the present form 
have been described above. The nephridia of HL. argenteus are not constricted at their 
passage through the septa, and the lumen forms a small number of regularly arranged 
and consecutive loops in the post-septal portion ; in the form under description there is 
