244 On the Blood-corpuscles of Mammalia. [Mar. 19, 



beautifully clear and homogeneous ; they commonly contain either one 

 or two nucleoli. It is from these cells that the blood-vessels of the tissue 

 are formed, and within them, red, and perhaps also, white blood-cor- 

 puscles become developed. 



Of the vacuolated cells above described some possess a distinct reddish 

 tinge, either pretty evenly diffused over the whole corpuscle, or in one or 

 more patches, not distinctly circumscribed, but fading off into the sur- 

 rounding protoplasm. Others contain either one, two, or a greater num- 

 ber of reddish globules, consisting apparently of haemoglobin. These vary 

 in size, from minute specks to spherules as large as, or even larger than, 

 the red corpuscles of the adult : in cells which are apparently least deve- 

 loped it is common to find them of various sizes in the same cell ; whereas 

 cells which are further advanced in development are not uncommonly 

 crowded with haemoglobin-globules, tolerably equal in point of size, and 

 differing from the adult corpuscle only in shape. It is important to re- 

 mark that there is, at no time, an indication of any structure within the 

 globules resembling a nucleus : the nucleus of the cell also appears, up to 

 this point at least, to undergo no change. In fact the formation of the 

 haemoglobin-globules reminds one rather of a deposit within the cell- 

 substance such as occurs in developing fat-cells, the difference being that 

 in the latter case the deposited globules eventually run together into one 

 drop, whereas in the former they remain distinct as they increase in size 

 and eventually take on the flattened form. 



Before, however, this change occurs in the haemoglobin-globules, the 

 cells containing them become lengthened, and are soon found each to 

 contain a cavity, within which the globules now lie. This cavity is pro- 

 bably formed by a coalescence of the vacuoles of the cell, or, what amounts 

 to the same thing, by the enlargement of one vacuole and the absorption 

 of the rest into it. The cell now comes to resemble a segment of a ca- 

 pillary, but with pointed and closed extremities ; it is of an elongated 

 fusiform shape, and consists of a hyaline protoplasmic wall (in which the 

 nucleus is imbedded) enclosing blood-corpuscles in a fluid blood, in fact. 



Two or more such cells may become united at their ends, a communi- 

 cation being established between their cavities ; indeed, by aid of branches 

 sent out from the sides a number of cells may unite to form a complete 

 plexus of capillary vessels containing blood, and situate at a considerable 

 distance in the tissue from any vessels in which blood is circulating. 

 Eventually, however, these last become united with the newly developed 

 capillaries, and the blood contained in the latter thus gets into the 

 general circulation. 



"With regard to the mode of junction of the capillary-forming cells with 

 one another, and with processes from preexisting capillaries, it has seemed 

 to me to occur most commonly, not by a growing together of their ex- 

 treme points, as commonly described, but rather by an overlapping and 

 coaptation of their fusiform ends, which, at first solid, become subse- 



