PROFESSOR OWEN ON THE OVA OF THE ECHIDNA HYSTRIX. 
1053 
hair pencil rolled the ovum out of its cell; there was no organic adhesion between 
them. 
In Plate 39, fig. 4, the ovum is shown, moderately magnified. The outer membrane 
(hyalinion or “ zona pellucida”) closely resembled that of the similar-sized ovum of the 
Ornithorhynchus paradoxus* * * § Under a magnifying power of 120, hyaline corpuscles 
with interspaces, as shown in fig. G, pervaded the homogeneous part of the tunic. The 
space separating it from the embryonal or vitelline mass is shown at the rent of the 
hyalinion, at h, fig. 4. No trace of spermatozoa could be detected in the fluid 
occupying the interspace. 
The yolk or germ-mass has a delicate smooth covering closely attached to the 
subjacent mass. On picking off with a fine needle-point part of this investment 
(fig. 5, v), the granular yolk-substance adhered to its inner surface. The chief and 
interesting feature of this yolk-mass was the linear fissure, g, extending along about 
one-third of the periphery, and penetrating a short way into the vitelline or germinal 
substance. This fissure may be interpreted as the commencement of the primary 
fission of the mass, and as indicative of a stage in development prior or preparatory to 
the complete fission observed by Barry t and BischoffJ in the smaller uterine ovum 
of the rabbit. 
Not any trace of embryonal structure was discernible in or near this fissure, or in 
any other part of the germ-mass. One portion of this mass presented a darker tint 
than the rest, but the structure was uniformly and minutely granular; the coagulating 
influence of the alcoholic menstruum had given increased firmness to the mass. 
The results of the foregoing investigations may be summed up as demonstrating the 
close resemblance in Echidna to Ornithorhynchus of the uterine ovum in structure, as 
in augmentation of size prior to embryonal development; the latter character being 
exemplified in a greater degree in the present [Echidna) series by the smaller size of 
the ovum, the least of the three, in the left uterus (Plate 39, fig. 1). Concomitantly 
with the more equal development of the right and left female organs in Echidna, as 
compared with Ornithorhynchus, § is the evidence of an ovipont by the right ovarium 
shown by the reception of the impregnated ovum in the uterus of that side (ib., 
fig. 3). 
Finally, the additional evidence of the viviparity of the Monotremes in the com¬ 
mencement of the fission of the germ-mass (fig. 5, y ). 
* This “ membrane (Plate 25, fig. 6, a) offered a moderate degree of resistance when torn open, and 
yielded equally in every direction when separated from the yolk, the rent margins curling inward like the 
coat of an hydatid ; it was of a dull greyish colour, slightly transparent.”—Phil. Trans., 1834, p. 561, 
t Phil. Trans., 1839, pp. 320-332. 
J ‘ Entwickelungsgeschichte der Kaninchen-Eies,’ 4to., 1842. 
§ Phil. Trans., 1834, Plate 25, fig. 2; Phil. Trans., 1865, Plate 41, fig. 1. 
