N"- I] BLOOD CORPUSCLES. 5« 



cells form the walls of the single median cardinal vein, which 

 anteriorly splits into the two posterior cardinal veins. More- 

 over, from this central mass of embryonic corpuscles cords of 

 similar cells branch off toward the yolk on either side, forming 

 the outlines of new blood-vessels (veins), and serving as centres 

 of origin for new red corpuscles. Both authors believe that 

 these embryonic blood corpuscles are capable of multiplication, 

 since karyokinetic figures are not unfrequently seen. The 

 first red corpuscles, according to this view, are true mesoblastic 

 cells, set apart for the formation of certain veins as well as 

 red corpuscles. Most English embryologists, on the contrary, 

 adhere to the view proposed by Klein {9), Balfour (10), etc.,' 

 a general account of which is given in Foster and Balfour's 

 Embryology of the Chick. According to this theory, the blood- 

 corpuscles are formed endogenously within large mesoblastic 

 cells found chiefly in the area vasculosa and area pellucida. 

 These cells send out processes which unite, forming thus a 

 protoplasmic network. At the nodal points of this network 

 the nuclei of the original cells multiply, to form groups. The 

 protoplasm around each of these assumes a red color from the 

 development of hagmoglobin, and the groups eventually break 

 up to form nucleated red corpuscles. By a similar method, 

 blood corpuscles are formed in the connecting processes, while 

 some of the protoplasm remains granular and uncolored, form- 

 ing the walls of the future vessels. The nuclei scattered along 

 the walls are also derived, like the corpuscles, from the nuclei 

 of the original mesoblastic cells. The plasma in which the 

 corpuscles float is a secretion from the protoplasmic walls of 

 the newly formed vessels. 



Gensch (11) in a communication giving the results of some 

 work done under Kupffer upon the teleosts {Esox lucius and 

 Zoarccs viviparous) states that the first blood corpuscles de- 

 velop out upon the yolk beyond the boundary of the mesoblast. 

 In this region there is a layer of large plasmodium like cells 

 lymg beneath the epiblast, but not forming a continuous epithe- 

 lium. The cells become united to one another by processes, 

 and the blood corpuscles are constricted off from them, forming 

 the blood islands seen in the blastoderm. This layer of forma""- 

 tive cells is called by Kupffer the "secondary endoderm." The 

 theory differs from those previously mentioned not only in the 



