172 ROBERTS, ON BLOOD-CORPUSCLES. 
imbedded or set in the rim of the disc, like the jewel ina 
diamond ring; but sometimes it occupied various positions 
Fie, 1. 
A. Human blood. —_B. Fowl’s blood treated with magenta, 
on the flat surfaces, and when so placed the spot was difficult 
or impossible to detect. 
It commonly presented a ‘thickly lenticular shape; some- 
times it was square, and occasionally in appearance vesicular, 
(Fig. 1, A, a.) In some instances, and especially in long-kept 
specimens, the particle was seen to stand out on the outhne 
of the disc like an excreseence. Still more rarely, instead of 
a spot, a thick red line ran round the circumference for a 
quarter or a third of its extent. (Fig. 1, A, 0.) 
As a rule, it was extremely minute, covering generally not 
more than a twentieth or thirticth of the circumference; but 
there was a considerable variation in its magnitude and dis- 
tinctness. Very rarely two specks could be seen; but the 
occurrence of adhering granules rendered the verification of 
this point extremely difficult. 
This description applies, so far as the inquiry has yet been 
prosecuted, to the mammalian blood-dise generally, making 
allowances for differences in size. In the camel the macula 
occupied indifferently any part of the oval outline. 
Among the oviparous classes, the blood of the fowl, frog, 
dace, and minnow, has been most fully examined (see fig. 1, B); 
but the blood of the sparrow, duck, goose, and turkey, was 
also searched, as well as that of the newt and carp. 
In all of these a tinted particle appeared, more or less 
constantly, in the cell-wall, when the corpuscles were treated 
with magenta.* The presence of a central nucleus in these 
* Tn order to bring out the best results, it was found requisite te modify 
tle strength and quantity of the solution for the different kinds of blood, 
