548 
DR. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
between the ovary and the orifice of its oviduct. The ducts follow the base of the ovary 
and the course of the ureters, and coalesce immediately before their termination in the 
urinal cloaca. In the mature female, during the breeding season, I found their internal 
structure to be the following. The mucous membrane clothing the duct in the posterior 
3 inches of its course (fig. 1, p) is raised into numerous transverse folds from 1 to 2 
millims. deep, with a sharp margin, closely set, parallel to one another, and more oblique 
anteriorly than towards the end of the oviduct. So far its structure is extremely similar 
to that of Menopoma. Further above, the duct changes its appearance. Its wall conti- 
nues to be highly turgescent, and to have a thickness of about 3 millims. ; but its sub- 
stance, instead of being a firm and resistant membrane, like the posterior portion, is a 
gelatinous mass enclosed in the thin fibrous outer membrane of the duct. This gelati- 
nous mass (which is the mucous membrane) is deeply longitudinally fissured ; and when 
the duct is cut through transversely (fig. 3), the fissures appear to the naked eye as 
numerous strise, radiating from the central canal towards the periphery. On a closer 
examination we find that the transverse folds of the hindmost portion of the duct gra- 
dually assume, towards the middle of its length, a more oblique, and finally a longitudinal 
direction ; they become very thin, semitransparent lamellae, are easily ruptured, very 
closely packed, and therefore much more numerous. In a section made transversely 
through the lamellae, but in the longitudinal axis of the duct (fig. 5), they appear like 
undulated bands (sometimes with short branches), with a linear tract of fibrous tissue 
{b) along their centre, into which blood-vessels extend, and which is the basis for a thick 
stratum of epithelial cells (c). In a second section, made right across the duct (fig. 4), 
the lamellae appear as slightly attenuated cones, again with the epithelial stratum (c) 
and the dark tract ( b ) in the centre, the latter being a continuation of, or proceeding 
from, the outer fibrous coat (a) of the oviduct. 
It was of interest to know whether the similarity in structure observed in the lower 
part of the oviducts of Ceratodus and Menopoma extended into the middle and upper 
portions. This is not the case. In a female Menopome, sexually mature, but killed 
out of the breeding season, the mucous membrane of those parts of the duct is not 
lamellated, but perfectly smooth, and in a section (fig. 6) through the wall in the lon- 
gitudinal axis the lumina of the cavities of numerous tubular glands are seen. 
The question naturally arises whether the condition of the oviduct described above, 
especially the gelatinous consistency of its wall, is not partly due to imperfect preserva- 
tion of the specimen. I can hardly believe that this is the case, because the neighbour- 
ing parts have not suffered from decomposition, and even the epithelium has been pre- 
served in its natural position and continuity. But when we find the mucous membrane 
turgescent with gelatinous matter, we may reasonably suppose that its secretion is of a 
similar nature, and destined to form a protecting case for the ova during their passage 
through the duct, as in Batrachians*. 
* Whilst my examination was limited to a female 26 inches long, the undeveloped sexual organs of which 
will be described on the following page, I expressed the belief that the ova might be expelled through the 
