ORIGIN OF VASCULAR TISSUES 79 



is difficult to imagine a process by which such a condition could 

 have been attained. Verocay explained the existence of multi- 

 ple hearts on the following basis as Rabl and others had pre- 

 viously done: there may have been a failure of the lateral anlagen 

 to fuse; also since each of the lateral heart anlagen normally is 

 a single vitelline vein, it is conceivable that individual hearts 

 had been formed from the rootlets of vitelline veins or from 

 multiple vitelline veins. Graper points out the fact that in the 

 preparation which Verocay studied there were present several 

 compact knots of liver tissue ' 'which did not represent a muti- 

 lated Uver, but seemed to be a case of multiplicatis hepatis 

 together with multiplicat'is cardis." Such a condition could be 

 explained on the assumption that the venous rootlets or multiple 

 veins had individually been surrounded and invaded by hepatic 

 proliferation from the wall of the gut. Conditions such as these 

 serve to emphasize the importance of the influence of develop- 

 ing parts on each other — a class of phenomena too often over- 

 looked and greatly underestimated. 



Graper attempted to prove experimentally that duplicate 

 hearts result from a failure • of the bilateral anlagen to fuse. 

 This he did by a median incision prior to heart-formation. None 

 of the conditions figured by Graper give a clue to the formation 

 of more than one heart-anlage on each side. My figures 28 and 

 29 may perhaps be of interest in this connection. None of my 

 experiments has approached the possibility of producing a seven- 

 hearted condition. 



/. The dorsal aorta. Meroplasts produced by longitudinal in- 

 cisions extending well into the posterior region yielded more or 

 less perfectly developed dorsal aortae which could be traced, 

 sometimes continuously, sometimes discontinuously, to the un- 

 doubted dorsal aortae of the head-region. Such findings are of 

 importance owing to the fact that it has been regarded as proved 

 by injection (Evans) that the dorsal aortae of the chick are 

 formed by longitudinal fusion of the elements of the mesial 

 border of the vitelline plexus. Figures 30, 31, 32, 33 and 34 

 show dorsal aortae or aortic anlagen which were certainly not 

 formed from a vitelline plexus, but are local formations. Such 



