Royal Microscopical Society. 17. 
Of the morphological development of the embryo of the small 
normal ovum, I have little to say ; as it was not my particular 
subject of study in this case. I rather directed my attention first 
to the examination of the umbilical vesicle in its fresh condition. 
This examination, together with the removal of the ovum from the 
membrana decidua and the execution of the sketches, occupying all 
the time which I had at my disposal until twilight, I was obliged 
to put the specimen in a weak solution of chromic acid for preser- 
vation. In -resuming my examinations on the next day, the body 
of the embryo had so much lost in transparency by the action of 
the chromic acid, that I was obliged to use compression in order to 
render it sufficiently transparent for microscopical observation. The 
compression of course would obliterate the form of any rudimentary 
internal organ. The whole embryo seemed to consist only of a 
multitude of small embryonic nuclei imbedded, or held together by 
a homogeneous plasma. With the fact of the developed blood- 
vessels in the chorion, however, before us, there can remain no 
doubt as to the existence of such within the body of the embryo; 
though I believe, as I have said before, that the larger vessels, as 
aorta, &c., being developed simultaneously with other internal 
organs, consist at this period, like the latter, only of embryonic 
nuclei imbedded in the plasma, until a differentiation of the various 
tissues commences. 
Those three prominences on the anterior side of the body of the 
embryo, representing, as I supposed, the rudimentary heart, were, 
as before mentioned, of a decidedly reddish tint, which was fading 
towards the body of the embryo. The question arises here, whe- 
ther this tint was the natural colour of the tissues, or whether it 
was due to the blood, which had been circulating within the tissue. 
As has been stated, my examination of the walls of the umbilical 
vesicle showed no coloured elements whatever ; still, as the specimen 
was examined in water, we might venture to suppose that those 
small round nuclei, which undoubtedly represented the coloured 
corpuscles in their earliest condition, had already possessed the 
characteristic colouring material, and lost it again by the action of 
the water. This supposition would explain the phenomenon, as in 
the absence of any muscular fibre formed, the reddish tint could 
hardly be due to the embryonic tissue itself, without the presence 
of the colouring element of the blood. 
During the whole course of my researches made on embryonic 
tissues, I have endeavoured to discover some general law concerning 
the different modes of multiplication of nuclei during embryonic 
life ; that is, whether one or the other process of multiphcation 
would regularly appear only during a certain period of the develop- 
ment of the embryo. This seems to be the case, however, only 
to a limited extent. During the earliest periods of embryonic 
c 2 
