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 only 

 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 (b). 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 (h). (i.) The stomach. (&.) Intestine. (I.) 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 (/?) and with the oviducts (g) enlarged with secretion, for the for- 



