CAPILLARY VESSELS. , 157 
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 pig- 
ment-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 lie above them, 
for when, as is the case in many larve, 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 suppo- 
sition 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 ad- 
duce these cells as proof of the existence of primary cells of 
capillary vessels. The uncertainty which attaches to the ob- 
servations on this poimt 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 dis- 
tinctly 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- 
