HIGHER INVERTEBRATES AND AMPHIBIA 225 



another individual of the same species; this kind of transplantation appar- 

 ently succeeded also between different species if they were nearly related 

 (Hydrophilus and Dytiscus), but not between farther distant species. Finkler 

 states that the head thus transplanted determines to a large extent the sexual 

 reflexes and the color of the body in the host. But other investigators were 

 not successful in repeating these experiments, and according to Przibram no 

 connection takes place between the nerve strands of the grafted head and the 

 body. 



As to echinoderms, these organisms are very unfavorable for transplan- 

 tation experiments on account of their rigid integument, and very few 

 investigations have been reported. However, Przibram succeeded in homoio- 

 transplantation of the disc in crinoids ; also in transplanting this organ into 

 other varieties differing from each other in their color; and even in the 

 starfish H. D. King accomplished, in one exceptional case, a homoiotrans- 

 plantation, in which however the ectoderm of host and transplant was the only 

 tissue which underwent union. 



As far as we can judge from the relatively limited number of experiments 

 in arthropods and echinoderms, these organisms seem to behave in a similar 

 way to lumbricidae as far as manifestation of organismal differentials is 

 concerned, provided we disregard more or less accidental difficulties in trans- 

 plantation due to peculiarities in the structure of these animals. On the other 

 hand, the difference between the results of homoiotransplantation and hetero- 

 transplantation of ovaries in the experiments of Kopec indicates that, after 

 all, the sensitiveness to heterodifferentials may be greater in this class than in 

 lumbricidae, and that the reactions of the host against the strange transplant 

 may be more complex. We have furthermore to consider the possibility that 

 the relatively low degree of regenerative power which these organisms possess 

 may render the manifestation of a reaction against transplants possessing a 

 different organismal differential more difficult than in lower organisms. 



In evaluating the relative significance of organismal differentials in the 

 various classes of animals which we have analyzed so far, we must in addition 

 to the complications already mentioned, take account of the fact that our 

 estimates as to reactions against strange differentials are based largely on a 

 gross study of the grafts. A study of the finer cellular reactions, which may 

 have occurred, is lacking, and if undertaken it might have made possible a 

 finer gradation of the organismal differentials. As stated, auto- and homoio- 

 transplantation show no marked differences in results in these various classes 

 of animals, and even heterotransplantation succeeded in a number of cases 

 between more nearly related species. In these respects the different classes 

 so far considered have behaved in a similar manner. 



Much more pronounced were the differences in the rigidity of organization 

 and in the possibility of inducing new organ formation or of transforming 

 one organ into another in these types of animals. As regards these reactions, 

 we find a definitely graded series, beginning with the hydroids and ascending 

 by way of planarians to the annelids and then to the arthropods. In the latter, 

 only small parts of the body can undergo far reaching changes; we refer in 



