previous to their union with the actual capillaries. Now it
is certain that a great many stellate cells are found in the
tail of the tadpole. They lie beneath the epithelium and pigment-cells on the same plane with the capillary vessels; are
smaller than the pigment-cells, and contain a colourless or
palish yellow substance; they send off processes on different
sides, which vary in number very much in different instances,
but are generally short, and for the most part do not join
with processes from other cells. Their shape has no sort of
connexion with that of the pigment-cells which le above them,
for when, as is the case in many larvae, the latter only send
off prolongations on two sides, these cells exhibit several pro-
cesses on different sides. They cannot, therefore, be young
pigment-cells. Such branches of the capillaries, as those at d,
sometimes appear to be connected with one of those stellate
cells, and the others might, therefore, be regarded as young
cells of capillary vessels which had not as yet begun to
anastomose. ‘These anastomoses, however, are not sufficiently
evident to enable me positively to assert their existence. The
great number of these stellate cells, and their presence at all ages
of the tadpole, are also circumstances unfavorable to the supposition that they are primary cells of capillaries. They might,
indeed, be conceived to indicate a lower stage of development,
as not having yet undergone any change, and that eventually
capillary vessels may be developed from some, whilst others
continue their existence without such a transformation, and
fill the place of cells of areolar tissue. That, however, would
be somewhat too hypothetical, and I shall, therefore, not adduce these cells as proof of the existence of primary cells of
capillary vessels. The uncertainty which attaches to the observations on this point in the tail of the tadpole appears, however, to be removed when we examine the incubated
hen’s egg.
4, When the germinal membrane of an hen’s egg which has been subjected to thirty-six hours’ incubation (at which period the formation of red blood has commenced, and is distinctly perceptible), is placed under the microscope, and the area pellucida examined with a magnifying power of 450, the capillary vessels are readily distinguished in it by their yel-
