262 PEOGRESS OF MICROSCOPICAL SCIENCE. 



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 corpuscles 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 

 surrounding protoplasm. Others contain either one, two, or a greater 

 number 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 developed it is common to find them of various sizes 

 in the same cell ; whereas cells which are further advanced in develop- 

 ment are not uncommonly crowded with hfemoglobin globules, toler- 

 ably equal in point of size,"^ and differing from the adult corpuscle 

 only in shape. It is important to remark 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 re- 

 minds 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 eventii- 

 ally take on the flattened form. Before, however, this change occurs 

 in the haemoglobin globules, the cells containing them become length- 

 ened, and are soon found each to contain a cavity, within which the 

 globules now lie. This cavity is probably formed by a coalescence of 

 the vacuoles of the cell, or, what amoimts 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 capillary, but with pointed 

 and closed extremities ; it is of an elongated fusiform shape, and con- 

 sists 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 communication 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 tissiie 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 pre- 

 existing capillaries, it has seemed to the author to occur most com- 

 monly, not by a growing together of their extreme points, as commonly 

 described, but rather by an overlapping and coaptation of their fusi- 

 form ends, which, at first solid, become subsequently hollowed by an 

 extension into them of the cavity of the cell or capillary, the partition 

 between the two being finally dissolved. 



