1'i.vri: I, XXVI 



Fid. 181. Section of eml>ryo of chick at the beginning of the second day, in the neighbourhood of the 



heart, a f the central nervous system, d. Under or epithelial 



glandular layer. I'. Anterior intestine (Vorderdarin). <\ Lninina serusa. f. Lamina ventralit. g. Aortse. k. Vence 



K.ild of anmios. /> ricuro-pt ritoneal cavity. H. Heart cavity, h. Endothelium of wall of 



heart, c'. Proper wall of heart. *. Blood corpuscles. 



PIG. 187. Transition of the formative elements of the blastoderm into endotlieli.il vesicles containing blood 

 corpuscles (endogenous development f hlood corpuscles), i. Coarsely granular forinativ.- clcinont in wliicli 

 is(ilali-(l nuclei, it, are fmiml. 2. Nunn'ruiis nm-l.-i. anil a fi-\v lilood corpuscles, a, are dist iii'.'uislialilc. while a 

 peripheral cone, .Hated from the rest of the fell. In ;. the peripheral nucleated layer 



of finely granular protoplasm has liecmipe distinct from the contents, which consist entirely of coloured 



1)1 1 corpuscles, so that we have before us a vesicle lined with cndothcJimn and tilled with 



The liniii}? of finely granular protoplaKin. with its more or less regularly iirntngcd nuclei, represents the 

 eudothelium of a future 



