1893.] NATURAL SCIENCES OF PHILADELPHIA. 81 



As stated in the earlier part of this paper, the regenerative power 

 seems, in low and primitive forms, and also in the very early stages 

 of the highest, as shown by von Jhering in the development of 

 Armadilloes, by what he calls temnogeny, or normal- division and 

 complete separation of the cells of the fertilized egg, to be most 

 completely represented in the early blastomeres or the products 

 of the early segmentations. In the next grade of organic types, 

 Porifera and Coelenterata, there appears to be a wider exten- 

 sion upon the whole organism and its parts of this regenerative 

 power. In bryozoa and echinoderms there is still in many forms 

 more or less of this regenerative power distributed throughout the 

 organism, but as specialization proceeds it seems to become less 

 marked, and if there is disturbance of the mode of development of 

 the Bilateralia, besides the apparently normal consecutive or linear 

 gemmation as in Monotus, Myrianida and Autolytus, there is devel. 

 oped a tendency to double the axis so that branched or coherent 

 double individuals arise. This reaches a most remarkable expres- 

 sion amongst Syllid worms, as worked out by Professor Mcintosh, 

 and may even extend to an early stage, as in the case of the produc- 

 tion of double embryos in Lumbricus, according to Kleinenberg. 

 In both the arthropod and vertebrate series disturbances of early 

 embryonic development, affecting the order and relations of the 

 karyokinetic processes in the blastoderm, are productive of double 

 monstrosities variously fused, according to a law which has been to 

 some extent defined by Rauber. 



As we proceed in our review of the successively higher groups we 

 find that this purely regenerative power becomes less and less 

 marked. In some worms, for example, the head may be regenerated 

 if cut off. It is doubtful whether this would be possible with even 

 the lowest vertebrate. In the vertebrates and arthropods or highest 

 Bilateralia, the regenerative power is reduced to the power of repro- 

 ducing lost digits or entire appendages, as in Crustacea. In verte- 

 brates it is finally restricted in fishes, batrachians and reptiles to the 

 regeneration of the tail or the distal parts of the extremities in the 

 adult, and in the highest of these series, namely, birds and mam- 

 mals, the power of the adult to regenerate lost distal parts of the 

 extremities is also lost. Nevertheless, there remains in the tolerably 

 advanced embryos of these forms the power to respond in a remark- 

 able way to disturbances of the normal hereditary or regenerative 

 processes involving the distal parts of the extremities, such as the 



