THE GROWTH OF THE EMBRYO IN THE FROG. 
239 
equatorial or third great subdivision: this cleavage begins on the side of the yelk 
opposite to that at which the granular body is seen. 
After the completion of this equatorial division, the granular-like nucleated body 
is suddenly lost, and I have been unable to trace it further. But I am not inclined 
to believe that these bodies are simply dissolved in the fluid surrounding the yelk in 
the Invertebrata, according to the supposition of Van Beneden, Rathke, Quatre- 
fages and others ; supported as this view has been by Professor Bischoff*, who is 
inclined to think that such may be their ending in the Vertebrata. On the contrary, 
the regularity of their appearance at a given period, their presence at a particular 
part of the yelk, their special course on the surface, and their disappearance at a given 
stage of the yelk-changes, furnish a presumption of their greater importance. 
Van Beneden'|~ has already pointed out, notwithstanding his above-mentioned 
opinion, that it is on that side of the yelk of the Limax at which these bodies appear, 
that the body of the animal is afterwards formed. Also Dumortier^ had previously 
believed that the spherical bodies gave origin to the head and foot of the future 
animal. Although I am unable to specify the exact part which these bodies take in 
the formation of the embryo, all my observations on the eggs of the Frog and Toad 
have proved to me that they are usually, and perhaps invariably, at that part of the 
yelk at which the head of the embryo is afterwards formed. Their isolation from the 
yelk for a time, during which it is in a very disturbed state, and their constant locali- 
zation, with their subsequent disappearance in that part at which the head is after- 
wards to be developed, seem favourable to the conclusion that their function is as 
definite as their presence is certain. 
It has been supposed by F. Muller § that the spherical bodies determined in the 
Mollusca the line of the first cleavage of the yelk ; and with this idea he named them 
the direction vesicles. But my observations on the development of the embryo lead 
me to believe, that, though the transit of these bodies is usually in the same line as 
the first cleft, the direction of the fissure is not determined by them, but is owing to 
some other cause. 
With the view of tracing the origin of these bodies, the egg of the Frog and Toad 
was examined from a period before the disappearance of the germinal vesicle to the 
time at which they appear on the yelk after fecundation ; and for this purpose the 
eggs were hardened in rectified spirit and then dissected |j. * # * * * 
* # #*#*###*##**# 
* Entwickelungsgeschichte des Meerschweinchens, 1852, p. 19, 
t Ann. des Sci. Nat., tom, xv. p. 126, and plate 1, 1841 ; and Muller’s Archiv for 1841, p. 181. 
+ Mem. de l’Acad. de Bruxelles, tom. x. p. 136. § Wiegmann’s Archiv for 1848, p. 1. 
|| [The results obtainable from this inquiry are not apparently contained in the MS. note books. It is how- 
ever well known to the writer that Mr. Newport intended, had his life been spared, to employ those means 
in learning the destination of the spherical bodies ; and the circumstance is here mentioned because the 
mode of investigation seems most judicious, and likely to be useful to any one engaged in prosecuting the 
inquiry. — G.V.E.] 
