Septembbe 14, 1900.] 



SCIENCE. 



395 



rived at, and indeed one does not see 

 how it is possible to obtain it, of the length 

 of years which might be required to eon- 

 vert a variation, capable of being trans- 

 mitted, into a new and definite specific 

 character. 



The circumstances which, according to 

 the Darwinian theory, determined the per- 

 petuation by hereditary transmission of a 

 variety and its assumption of a specific 

 character depended, it was argued, on 

 whether it possessed such properties as en- 

 abled the plant or animal in which it ap- 

 peared to adapt itself more readily to its 

 environment, i. e., to the surrounding con- 

 ditions. If it were to be of use the organ- 

 ism in so far became better adapted to hold 

 its own in the struggle for existence with 

 its fellows and with the forces of nature 

 operating on it. Through the accumulation 

 of useful characters the specific variety was 

 perpetuated by natural selection so long as 

 the conditions were favorable for its exist- 

 ence, and it survived as being the best fitted 

 to live. In the study of the transmission 

 of variations which may arise in the course 

 of development it should not be too exclu- 

 sively thought that only those variations 

 are likely to be preserved which can be of 

 service during the life of the individual, or 

 in the perpetuation of the species, and 

 possibly available for the evolution of new 

 species. It should also be kept in mind 

 that morphological characters can be trans- 

 mitted by hereditary descent, which, 

 though doubtless of service in some bygone 

 ancestor, are in the new conditions of life 

 of the species of no physiological value. 

 Our knowledge of the structural and func- 

 tional modifications to be found in the 

 human body, in connection with abnormal- 

 ities and with tendencies or predisposition 

 to diseases of various kinds, teaches us that 

 characters which are of no use, and indeed 

 detrimental to the individual, may be he- 

 reditarily transmitted from parents to off- 



spring through a succession of genera- 

 tions. 



Since the conception of the possibility of 

 the evolution of new species from pre-exist- 

 ing forms took possession of the minds of 

 naturalists, attempts have been made to 

 trace out the lines on which it has pro- 

 ceeded. The first to give a systematic ac- 

 count of what he conceived to be the order 

 of succession in the evolution of animals 

 was Ernst Haeckel, of Jena, in a well- 

 known treatise. Memoirs on special de- 

 partments of the subject, too numerous to 

 particularize, have subsequently appeared. 

 The problem has been attacked along two 

 different lines : the one by embryologists, 

 of whom may be named Kowalewsky, Ge- 

 genbaur, Dohrn, Eay Lankester, Balfour 

 and Gaskell, who with many others have 

 conducted careful and methodical inquiries 

 into the stages of development of numerous 

 forms belonging to the two great divisions 

 of the animal kingdom. Invertebrates, as 

 well as vertebrates, have been carefully 

 compared with each other in the bearing of 

 their development and structure on their 

 afiSnities and descent, and the possible se- 

 quence in the evolution of the Vertebrata 

 from the Invertebrata has been discussed. 

 The other method pursued by paleontol- 

 ogists, of whom Huxley, Marsh, Cope, Os- 

 born and Traquair are prominent authori- 

 ties, has been the study of the extinct forms 

 preserved in the rocks and the comparison 

 of their structure with each other and with 

 that of existing organisms. In the at- 

 tempts to trace the line of descent the im- 

 agination has not unfrequently been called 

 into play in constructing various conflict- 

 ing hypotheses. Though from the nature of 

 things the order of descent is, and without 

 doubt will continue to be, ever a matter of 

 speculation and not of demonstration, the 

 study of the subject has been a valuable 

 intellectual exercise and a powerful stimu- 

 lant to research. 



