ITS DIFFERENT PHASES OF DEVELOPMENT IN THE ANIMAL SERIES. 
95 
Blood-corpuscles of the Medicinal Leech. 
51. The blood examined was obtained by making- incisions on the back or side of 
the animal after having carefully wiped the surface of the skin. In making these 
incisions care was taken not to cut into the stomach, or its csecal appendages, in 
order to obviate the possibility of foreign blood which might have been taken in as 
food, becoming mixed with the real blood of the animal itself. 
52. In the first place it is worthy of remark, that whilst the corpuscles of the blood 
of the Earth-worm are the largest which I have yet found in any invertebrate animal, 
the corpuscles of the blood of the Leech are the smallest. 
53 . When the blood of the Leech is examined under the microscope as soon after 
its abstraction from the animal as possible, numerous corpuscles are seen having the 
appearance of very pale, shining, colourless, fusiform filaments, about - goVo th °f an 
inch in length, and about y ^o uth of an inch in breadth, less or more (fig. 9.), suspended 
in the red-coloured plasma. Very soon, however, the corpuscles are seen gradually 
to become shorter and somewhat broader, until at last they acquire an irregular cir- 
cular form (fig. 1 0 .). 
54. In this state the majority of the corpuscles appear to be composed of a nucleus 
surrounded by a collapsed and shrivelled cell-wall. And that this is so, is reduced 
to a certainty by the addition of water, which causes the cell to become distended 
and to acquire a circular form, whilst the outline of the cellseform nucleus appears 
more distinctly defined (figs. 11 and 12 .). 
55. Thus distended, the cell is from 3 - oV oth to y gV oth of an inch in diameter, and 
the nucleus 70 * 0 0 th, or more. 
56. Many of the cells transmit the light slightly tinged red, as if there w T as some 
colouring matter lining their interior (fig. 12 .). 
5/. The corpuscles of the blood of the Leech now described, it will have been 
observed, are nucleated cells. 
58. Granule-cells . — Corpuscles in the blood of the Leech referrible to this head 
are few in number. Examples of them are delineated in figs. 7 and 8 *. 
* I subjoin here a description of the corpuscles of the blood vomited by leeches which have never been used. 
This blood I found to be composed of a coloured plasma, and numerous corpuscles having a considerable 
resemblance to those of the blood of the animal itself after having lost their original fusiform shape, and become 
somewhat distended by water. On the whole, however, the corpuscles of the blood in question were somewhat 
larger, and appeared perhaps better defined than those of the Leech itself, especially the granule-cells, which 
were also more numerous, though still not so numerous as the nucleated cells. 
Of the granule-cell there were both coarsely and finely granular stages (figs. 13 and 14.). There were 
cells in transition from the granule to the nucleated phase (fig. 15.). The nucleated cells (figs. 16, 17 and 18.) 
were most of them circular, but some were oval. Most appeared tinged red in their interior, those which did 
not had their cell-wall so very pale that it was apt to be overlooked. 
The blood contained in the stomach of leeches which have not been used, and of which I have now briefly 
described the corpuscles, from what animal is it derived ? The resemblance of the blood to that of the animal 
itself suggests the probability that medicinal leeches suck the blood of some other kind of leech. That they 
suck each other’s blood has been positively denied by Dr. Rawlins Johnson. 
MDCCCXLVI. O 
