Cuar. I. THE PURKINJEAN VESICLE. 477 
all circumstances flat, as if disciform (Pl. 8, fig. 15a, f"). These latter features 
obtam at a time when the egg is about from one eighth to one sixth of an 
inch im diameter; but subsequently, at no very distant period, the Wagnerian 
vesicles and their contents disappear, and give place to a homogeneous fluidity, 
which generally pervades the Purkinjean vesicle, and lasts for the remainder of 
its existence. However, this rarely happens in much smaller eggs; yet an egg 
with a diameter of one tenth of an inch (Pl. 9, fig. 1) may have a Purkinjean 
vesicle, (fig. la, 4,) which, although perfectly free from Wagnerian vesicles, equals 
in size another Purkinjean vesicle containing numerous Wagnerian vesicles, (Pl. 9, 
fig. 5a, 5b, 5e,) and even belonging to a much larger ege (fig. 5). Respecting 
the presence of a wall inclosing the Wagnerian vesicle we have only to men- 
tion, that water breaks up its Valentinian vesicles into small, angular portions, which 
spread throughout its whole extent, though they stop within its outlines, (Pl. 8, 
fig. 24b, a, a; Pl. 9, fig. 4b,) evidently because of a resistant substance which does 
not yield to the reaction. This certainly is enough to substantiate the existence 
of a membrane, and moreover of one that has considerable stability, when we 
see that an hour's maceration, in one instance, did not destroy its entity (Pl. 
9, fig. 4b). While speaking of the reaction produced by water, we may as well 
mention also, that heat applied by boiling does not seem to effect an appreciable 
change in the intimate constituents of the Wagnerian vesicles, but evinces its dis- 
turbing power in another manner by loosening them from the wall of the Pur- 
kinjean vesicle, and forcing the whole to cluster around the centre of the latter 
(Pl. 9, fig. 5a, 5b, 5¢) in the form of a nebula. 
The Purkinjean vesicle durmg all this time has been rapidly increasing in 
size, and becoming more and more easily recognizable externally, till, at the last- 
mentioned size of the egg, namely, when it has one sixth or one fifth of an inch 
in diameter, it may be taken from the bed of yolk in which it lies, without 
any other guide than the naked eye. But, on account of the excessive tender- 
ness of the membrane of the Purkinjean vesicle, it is not possible to effect this, 
unless it be boiled within the egg, when the heat coagulates the albuminous 
contents to a sufficient consistency to allow its being lifted up on the point of 
a knife; but even then it hardly holds together, thus evidently evincing the pres- 
ence of a smaller amount of albumen, and a greater quantity of oily substance, than 
can be found in older ones. In two eggs of this size that were opened after 
having been boiled, the side of the Purkinjean vesicle that laid next to the yolk 
sac was inverted slightly, (Pl. 9, fig. 5b,) probably owing to the contraction of 
the contents, and the pressure of the yolk. This phenomenon occurs to a greater 
extent in older eggs, and is obviously due to the increased amount of albumi- 
oo” 
nous deposit, judging from the greater toughness of the Purkinjean vesicle when 
