242 
MR. NEWPORT ON THE IMPREGNATION OF 
spermatozoon with the envelopes of the ovum, seems closely to resemble that of the so- 
called catalytic power of certain known bodies, in so far as that contact, during onlv 
very short spaces of time, with the surface of the ovum, appears to be sufficient to in- 
duce certain changes in the interior. These changes, too, as known of catalysis, are 
carried only to a certain extent when the exciting agents, — in this instance the sper- 
matozoa, — are feeble in action or but very few in number ; and then, as we have seen, 
the yelk may become only more or less partially segmented ; or the changes in it, 
having proceeded to a certain extent, may then become arrested, apparently from de- 
ficiency of the originally exciting cause. Then, again, we find that although segmen- 
tation of the yelk may take place, embryos are not produced unless there has been 
some continuance or duration of contact of the impregnating with the impregnated 
body; and that the number produced seems to have reference to the duration and to 
the full sufficiency of the exciting cause. But neither what we at present know of 
the so-called catalytic power or of endosmosis, appears alone to be sufficient to ac- 
count for the whole of the phenomena of impregnation. Simple contact of the sper- 
matozoon does not appear to be sufficient to determine the transmission of more or 
less of the material structural characters of the male parent to the offspring ; while 
diffluence and endosmosis of the substance of the spermatozoon can hardly be ima- 
gined to occur in a brief second or two of time sufficiently to effect the full impreg- 
nation of the yelk, and induce its invariable consequence, segmentation. Possibly, 
we may hereafter find that the first changes induced by contact of the impregnating 
body are completed by its diffluence, and by the material constituents into which it 
is dissolved, being transferred to the yelk by endosmosis. 
Description of the Plate. 
PLATE XIV. 
Fig. 1. The female Frog, Rana temporaria, dissected to show the situation of the 
entrance to the oviducts (a) at each side of the heart {h). The liver (c) is 
drawn back and removed a little from its natural position to show the 
spaces {d) along which the ova pass from the cavity of the abdomen to the 
mouths of the oviducts (g), to be received into the dilated or uterine por- 
tion of the ducts (A), {i.) The stomach. (A.) Intestine. (/.) Colon and 
rectum, {m.) The bladder. 
Fig. 2. A portion of the commencement of the oviduct magnified, partially concealed 
by the root of the lung. 
a. The entrance to the duct between the heart and liver, (e.) The suspen- 
sory ligament of the liver. {/.) The base of the lung around which 
the oviduct (g) passes. 
Fig. 3. The female Frog, exhibiting the viscera in situ before the ova have left the 
ovaries {p) and with the oviducts (g) enlarged with secretion, for the for- 
