114 FRANKLIN P. REAGAN 



between the planes of figures 87 and 88. The mesenchyme stain- 

 ed clear blue while the erythrocytes stained red. Intervening 

 stages (Erthbl.) take a pui^ple stain. It seems altogether improb- 

 able that these erythrocytes have reached their present location 

 through the circulation. The only blood-vessel which could be 

 seen to approach this meroplast was a spur which projected 

 towards its anterior extremity, but never reached it. Also the 

 hematopoetic area is separated from the vessel by solid carti- 

 lage. The posterior region of the meroplast contains no vascu- 

 lar tissue. The transplanted tissue is bounded ventrally by a 

 compact sheet of muscle. 



Now this region of the yolk to which the meroplast was trans- 

 planted is one of those regions in which the mesoderm, accord- 

 ing to Stockard, is incapable of forming blood-cells. It is one of 

 those ''regions in which wandering blood anlagen never make 

 themselves manifest." If there was no circulation of the blood, 

 the erythrocytes must have differentiated locally. But this 

 mesenchyme is cephalic, and cephalic mesenchyme, according to 

 Stockard, can not form erythrocytes. The reader may judge 

 for himself which (if either) of these claims of Stockard seems 

 questionable in view of the conditions here described. 



The embryo from which the meroplast was removed was pre- 

 served at the time of operation and sectioned to make sure that 

 none of the intermediate cell-mass had been transplanted. The 

 posterior end of the meroplast proliferated a great deal of tissue 

 which evidently induced a very active migration of mesenchyme 

 from the posterior region of the 'host.' The region between the 

 two contains a considerable amount of tissue of a nondescript 

 sort. 



By no means is an attempt* made to estimate the value of this 

 experiment for the solution of the question at hand. The work 

 of transplanation has not been carried far enough to demon- 

 strate its true worth. Greater experience in the manipulation 

 of this method might lead to results which would be truly im- 

 portant. The main trouble lies in the extremely low viability of 

 the isolated tissue. 



