CAPILLARY VESSELS. 157 



previous to their union with the actual capillaries. Now it 

 is certain that a great many stellate cells arc found in the 

 tail of the tadpole. They lie beneath the epithelium and pig- 

 ment-cells on the same plane with the capillary vessels; arc 

 smaller than the pigmcnt-cclls, 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 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 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 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 dis- 

 tinctly perceptible), is placed under the microseope, and the 

 area pellucida examined with a magnifying power of 450, the 

 capillary vessels arc readily distinguished in it by their yel- 



