244 
DR. MARTIN BARRY ON THE CORPUSCLES OF THE BLOOD. 
large quantity. But in viviparous animals, these discs appear to produce little more 
than an object corresponding to that which in the Bird, for instance, has the form of 
the discus vitellinus. Fig. 173. presents these discs (g) rapidly dividing for the form- 
ation of the yelk in the Bird. — I refer to my First Series on the Embryo (/. c., Plate 
V. fig. 25. e) for the earliest appearance of the membrane of the yelk. 
195. The very minute ovisacs, myriads of which I described as found in the walls 
of the Graafian vesicle, seem to owe to the following circumstance their parasitic 
situation. The covering acquired by the ovisac consists of cellular tissue. Cellular 
tissue is formed out of corpuscles having the same appearance as corpuscles of the 
blood. But each of the minute ovisacs was once a young corpuscle of the same kind. 
And it appears that, while some of these corpuscles enter into the formation of the 
cellular tissue investing a large ovisac, other corpuscles are developed into smaller 
ovisacs, which therefore are found in the interstices of that tissue. 
196. I have already stated that the individual discs exhibit a reproducing property. 
This is the case as well with those discs that have begun to enter into the formation 
of a structure, as with those not yet appropriated, — that is, still in circulation. With 
regard to the former it is to be remarked, that, in many parts, red colouring matter 
is reproduced along with the new discs (par. 1 1 1.), giving them quite as deep a colour 
as the floating corpuscles themselves ; which in other respects also they resemble. 
Hence my general employment of the expression, having the same appearance as cor- 
puscles of the blood: for it was impossible to distinguish those corpuscles which had 
been themselves extravasated ; and I presume that, generally speaking, the term 
“corpuscles of the blood" would have been inapplicable to others, though immediately 
descended from them. 
19/. Recapitulation. 
1. The nucleus of the corpuscle of the blood admits of being traced into the pus- 
globule. 
2. The various structures arise out of corpuscles having the same appearance, form, 
and size as corpuscles of the blood. 
3. The corpuscles having this appearance, and giving origin to structures, are pro- 
pagated by division of their nuclei. 
4. The corpuscles of the blood, also, are propagated by division of their nuclei. 
5. The minuteness of the young blood-corpuscles is sometimes extreme; and they 
are to be found in parts usually considered not permeable by red blood. 
Postscript (June 23, 1841). 
198. Blood found in the heart (immediately after death by bleeding) often presents 
incessant alterations in the position of its corpuscles. When one of the corpuscles is 
