THE GROWTH OF THE EMBRYO IN THE FROG. 
235 
Mammalia, but their evolution has not hitherto been traced, nor their signification 
been understood*. 
I may now detail the results of an experiment carefully made for the purpose of 
ascertaining somewhat of their origin and destination; this one will serve as a type 
of all. 
On the 27th of March 1853, and at a temperature of 61° Fahr., three eggs were 
put in a cell and impregnated in the usual way. 
* A single spherical body, projected from the surface of the yelk and maintained for a period at a distance 
from it on a pedicle, was first noticed in Lymnaus stagnalis by Carus in 1824 (Von der iiusseren Lebensbedin- 
gungen der weiss- und kaltbliitigen Thiere, p. 33. t. i. fig. 4), before the investigations of Baer and Purkinje 
had directed attention to the structure of the ovum. But this pediculated body was not further regarded by 
Carus than as the imagined axis of rotation of the yelk. A similar body, but followed also by a second, was 
also seen in Lymnaus by Dumortier in 1837 (Mem. de l’Acad. de Bruxelles, tom. x. p. 136 ; also Annales des 
Sciences Naturelles, 2 me serie, tom. viii. 1837, p. 136), and this was immediately supposed by him to be the 
analogue of the Purkinjean vesicle, and with its fellow, was believed to give origin to the head and foot of the 
animal. A single body was also noticed in Lymnaus by Pouchet (Sur le developpement de l’Embryon des 
Lymnees, Comptes Rendus, July 1838, pp. 86, 87), and by him likewise was thought to be the Purkinjean 
vesicle set free from the yelk. But Sars observed two vesicles in Tritonia, Eolis and Doris (Wiegm ann’s 
Archiv, 1837), and Van Beneden found two in Limax agrestis (Muller’s Archiv, 1841, p. 180) and 
Aplysia clepilans (Annales des Sc. Nat. tom. xv. p. 126. pi. 1. figs. 4, 7, 9, 1841), and remarked that in both 
species these bodies come from the yelk before segmentation is commenced, and that their presence indicates 
that the body of the Limax will be formed on that side of the yelk at which they appear. Nevertheless Van 
Beneden, observing that they are suspended for a time in the transparent fluid which surrounds the yelk from 
which they proceed, believed that they become dissolved in this fluid and do not take any direct part in the 
formation of the embryo ; and although he appears to have regarded them as the representatives of the Purkin- 
jean vesicle, he seems to have doubted whether this body plays the important part which has been attributed 
to it in the higher animals. At the same time he called attention to the fact of the constancy of these vesicles 
in Lymnaus, Limax and Aplysia as meriting consideration. Yet Karsch, who afterwards saw the vesicles in 
Lymnaus (Wiegmann’s Arch. xii. 1846, p. 255), thought their presence an abnormal condition. The late 
Dr. J. Reid, however, saw them in Doris bilamellata (Annals and Mag. of Nat. Hist. June 1846), and F. Muller 
in the eggs of Limapontia (Wiegmann’s Arch. 1848, p. 1) ; and although Vogt failed to notice them in 
Actaon, he appears to have seen them in Limax, and his remarks (Ann. des Sc. Nat. 3 me serie, tom. vi. 1846) 
as to their disappearing in the albumen, coincide with those of Van Beneden. 
In theNudibranchiata, Nordmann appears to have observed at least one of the vesicles in Tergipes Edwardsii, 
although he refers to it as a little vesicle “ of air” separated from the yelk (Ann. des Sc. Nat. 3 me serie, tom. v. 
1846, p. 143). 
In the Acephalous Lamellibranchiata one vesicle at least has been noticed in several genera. It has been 
remarked by Qttatrefages in Teredo navalis (Ann. des Sc. Nat. 1848), by Loven in Modiolaria marmorata, 
Cardium pygmaum. Patella pellucida, and Solen pellucida (in Kongl. Vetenskaps-Akademiens Forhandl. 
Decem'b. 1848, and Muller’s Archiv, 1848, p. 531), and more recently by Kebf.r in Unio and Anodonta 
(De Spermatozoorum introitu in Ovula, Konigsberg, 4to, 1853). In Modiolaria and Unio the vesicle is re- 
moved from the yelk on a pedicle, as in Gasteropoda, and this Keber has miscalled “ a Micropyle while 
in Cardium, Patella, Solen and Teredo the vesicles rest on the surface of the yelk. Loven, who mentions 
that the germinal vesicle itself disappears in these mollusks before the eggs quit the ovary, has well remarked 
that the body seen on the surface of the yelk in the fecundated egg before segmentation, cannot therefore be the 
Purkinjean vesicle itself as supposed by Dumortier, and he ingeniously inquires whether it may not be its nucleus. 
In th t Annelida, as in Mollusca, one, and in some instances two, vesicles have been seen. Kolliker observed 
2 h 2 
