Royal Microscopical Society. 
13 
somewhat darker than the outer, represents the muscular coat, 
already tolerably advanced in development ; it also contains a con- 
siderable number of nuclei, with their long axes, however, at right 
angles to the course of the vessel. A number of these nuclei, 
though somewhat larger and of an oblong form, show, like those 
of the outer coat, a fine double contour, and are filled with 
granules. The rest, however, represent mother-nuclei, being dis- 
tinguished by a greenish lustre. A number of these bear those 
characteristic small vesicles or buds, which show that the process of 
their multiplication is still in active operation : the remaining ones 
appear in the form of irregular spindle-shaped bodies, with crescent- 
shaped notches, the traces of their former activity, in their contours. 
The muscular coat itself appears as a fine granulous substance. 
Besides those nuclei just described, a number of others of an oval 
form are observed on the inner surface of the vessels ; these probably 
represent the epithelium of the vessel in the process of formation. 
I shall next proceed to give an account of the results obtained 
from the examinations made on the very small ovum, alluded to in 
the beginning of this article. 
This was the smallest specimen of the human ovum I had ever 
seen. (Fig. 13.) Being removed from the membrana decidua, which 
had come away entire, it was found to be perfectly fresh and 
normal. Slightly oval in shape, it only measured 13 by 11 mm. 
in diameter. The oval form, however, may have been produced by 
a stretching of the membrana decidua, which was pinned down 
upon a cork during the operation of its removal. Its surface was 
almost entirely covered by villi. The embryo it contained (Fig. 14), 
measuring only 6 mm. in length, was bent upon itself, the inferior 
part of the spinal column making a spiral turn to the left side of the 
body. The rudiments of the vertebrae when examined through a 
lens (Fig. 15), manifested themselves in the form of opaque spots. 
The superior portion of the body was divided into three segments, 
the upper and larger one of which represented the future cranium, 
the two others visceral arches ; there was no trace of the formation 
of the eye or ear to be seen. Directly below the visceral arches, 
and occupying the middle portion of the body, there were three 
round prominences, which, as I suppose, represented the rudiments 
of the heart. (Figs. 15 and 17.) They were of a reddish colour, and 
the larger of them was, by a subsequent examination, found to be 
hollow. Below these prominences the pedicle of the umbilical 
vesicle was seen to arise from the rudimentary alimentary canal ; 
and still lower down, within the curve of the spinal column, also 
the umbilical vessels. The extremities manifested themselves only 
in the form of four small delicate buds ; the upper ones laterally 
and behind the above-mentioned prominences, and the lower ones 
within the curve of the inferior portion of the spinal column. That 
