294 LIONEL JAMES PICTON. 



Thus in position iu the circulation, as well as in appearance, 

 this irregular cord (fig. 4) corresponds to a heart-body. It 

 contains numerous yellowish pigment granules. 



Summary and Conclusions. 



It is undesirable to attempt as yet to form a theory of the 

 action of the heart-body accounting for the details of its 

 structure. The facts relate themselves to one another, and 

 suggest resemblances with other animals ; but the part the 

 organ plays in the economy cannot be defined : still there are 

 several indications of the broad outlines of its nature. 



First of all, with regard to its homologies, its mesoblastic 

 origin, shown at least in one instance, Polymnia, must be 

 considered. The organ is not homologous with the diver- 

 ticulum of the gut which projects into the dorsal vessel of 

 Buchholzia and other Oligochteta, and the theories of Horst 

 and Beddard to this effect fall to the ground. Nevertheless, 

 considering the fact that iu those forms the diverticulum of 

 the gut, as it pushes into the heart, must carry the heart wall 

 with its coelomic epithelial covering in front of it, it is evident 

 that the latter must form a part of the so-called " heart-body." 

 It is, perhaps, this mesoblastic part from which the anterior 

 part of the heart-body of Buchholzia is divided, and were this 

 the case there would be a partial homology of the organ with 

 that of Polychseta. Further, the heart-body described by 

 Nusbaum and Rakowski in Fridrica (25') appears to have no 

 connection whatsoever with the gut, and accordingly re- 

 sembles that of Polychseta in being entirely mesoblastic. 



The mesoblastic origin being established, the organ may be 

 regarded, as Eisig suggests, as of the nature of intra-vascular 

 chloragogen, — that is, as modified peritoneal tissue, primitively 

 clothing the outside of the dorsal vessel, but becoming folded 

 so as to lie within it. The word '^ chloragogen,^' however, must 

 be understood only as a descriptive term, Schaeppi having 

 shown that the granules occurring in tlie tissues included 

 under that designation are of ditfereut chemical natures. 



