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. HI.), 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 extra vasated ; and I presume that, generally speaking, the term 

 " corpuscles of the blood'' would have been inapplicable to others, though immediately 

 descended from them. 



197. 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 



