60 The American Naturalist. [January, 
The nuclei of the nucleated red corpuscles of the young embryo 
(except of the larger variety) are lost while in the circulation. . . . 
As the embryo grows larger, and the production of new corpuscles be- 
comes localized in different organs,—liver, spleen, marrow,—more and 
more of the early history of the corpuscles is passed over while still in 
the blood-forming organ, and more and more of the red corpuscles are 
sent into the blood in the non-nucleated stage. In the first part of 
embryonic life new red corpuscles are produced in the liver from 
groups of mesoblastic cells, outlining the position of future blood- 
vessels (veins). It is probable that new red corpuscles are formed 
in all parts of the body where blood-vessels are being developed.” 
This view of the origin is essentially different from that of Klein and 
Balfour, as given in the “ Embryology of the Chick,” where it is 
asserted that the red corpuscles are endogenously within large meso- 
blastic cells. ‘In the second half of embryonic life red corpuscles 
are formed in the liver, the spleen, and the marrow of the bones, the 
function being most active first in the liver, then in the spleen, and, 
finally, in the red marrow of the bones, where it continues during 
adult life. it 
“ The white corpuscles and blood-plates do not occur in the cire 7 
lating blood of young embryos, but make their appearance in later 
embryonic life.” Certain nucleated cells of the red marrow of the 
bones multiply by division, later loose their nuclei by extrusion, and 
getting into the blood become the red corpuscles, and the biconcavity — 
of these corpuscles may be due to the extrusion of the nucleus. 
The white blood corpuscles are derived from the lymph leuco- 
cytes. These enter the circulation, and are at first not amceboid. The 
nucleus increases in size as the leucocyte grows older ; finally it frag- 
ments, and probably this is followed by disintegration of the whole 
cell. The fragments of the nuclei persist for a time as the blood- 
plates. See Minot in NaTuRaLIST, November, 1890. 
Appendages of the First Abdominal Segments of Embryo- 
Insects.—Mr. Wheeler has made a comparative study of the larval 
appendages of the first abdominal segment of insects (Trans. Wisconsit 
Acad. Science, etc.) He concludes that the appendage—the pleuro- 
podia—of this segment were at one time organs of considerable fang 
tional importance in the primitive Hexapods, but are not equally well, 
represented in the larva of all existing groups. They are 5¢ 
homologous with the appendages of the thorax and 
and in the embryos of existing insects these rudimentary structures 
