Manchester Memoirs, Vol. I. (1906), No. 3. 81 



By the testimony, therefore, of all these authors 

 except Hepke, the original stomodaeum — which includes 

 the pharynx — and proctodaeum are replaced in the 

 regenerated parts by epithelia of ectodermal origin ; by 

 Hepke's account these epithelia are ectodermal but replace 

 (apparently) not only the stomodaeum and proctodaeum, 

 but originally endodermal portions of the digestive tract 

 as well. In either case it seems we are involved in a 

 contradiction. With regard to the new formation of the 

 mesoderm there is more agreement ; it is derived from the 

 epidermis, a fact which, once more, is out of harmony 

 with its embryonic development. 



It should be added that Dendy ^^^ has shown that in 

 Antedon the visceral mass can be regenerated partly from 

 the mesoderm, partly from the ectoderm of the calyx ; 

 the new alimentary canal arises from the latter. 



In this connection it may be mentioned that cases occur 

 in which tumours resembling one another in every respect 

 may, apparently, have been derived in one instance from 

 the ectoderm, in another from the mesoderm, or even the 

 endoderm. The most remarkable instance of this is, 

 perhaps, that quoted by Hansemann^^ where a malignant 

 growth of the epithelium of the gall-bladder had assumed 

 the structure of an epidermal cancroid. Many pathologists 

 have, therefore, given up the attempt to classify the 

 abnormal growths by reference to their developmental 

 origin. 



Last of all it remains for us to discuss the bearing on 

 our question of a very important series of facts which the 

 experimental embryology of recent years has made known 

 to us. 



6*« Stud. Biol. Lab. Owens College, vol. i, p. 299—312, 1886. 

 5^ " Die mikroskopische Diagnose der bosartigen Geschwiilste," p. 23, 

 Berlin, 1897. 



