164 



SCIENCE. 



[N. S. Vol. V. No. 109. 



placed him in the historj'^ of science on the 

 same line with Lamarck and Darwin. 



He states four lectures, p. 26, as follows : 

 " The results thus far obtained in the lec- 

 tures which I have delivered can be ex- 

 pressed as follows : There is a gradation of 

 type in the class of Echinoderms, and in- 

 deed in every class of the animal kingdom, 

 which, in its general outlines, can be satis- 

 factoriljr ascertained by anatomical investi- 

 gation ; but it is possible to arrive at a more 

 precise illustration of this gradation by em- 

 bryological data. The gradation of struc- 

 ture in the animal kingdom does not only 

 agree with the general outlines of the em- 

 bryonic changes. The most special com- 

 parison of these metamorphoses with full 

 grown animals of the same type leads to 

 the fullest agreement between both, and 

 hence to the establishment of a more defi- 

 nite progressive series than can be ob- 

 tained by, the investigation of the internal 

 structure. These phases of the individual 

 development are the new foundations upon 

 which I intend to rebuild the system of 

 zoologj'. These metamorphoses correspond, 

 indeed, in a double sense, to the natural 

 series established in the animal kingdom : 

 first, by the correspondence of the external 

 forms, and secondly, by the successive 

 changes of structure, so that we are here 

 guided by the double evidence upon which 

 the progress in zoology has, up to this time, 

 generally been based. 



" Their natural series again correspond 

 with the order of succession of animals in 

 former geological ages, so that it is equally 

 as true to say that the oldest animals of any 

 class correspond to their lower types in the 

 present day as to institute a comparison 

 with the embryonic changes, arid to say 

 that the most ancient animals correspond 

 with the earlier stages of growth of the 

 types which live in the present period. In 

 whatever point of view we consider the 

 animal kingdom, Ave find its natural series 



agree with each other ; its embryonic phases 

 of growth correspond to its order of suc- 

 cession in time, and its structural grada- 

 tion, both to the embryonic development 

 and the geological succession, corresponds 

 to its structure ; and if the investigations 

 had been suflBciently matured upon this 

 point, I might add that all these series 

 agree also in a general way with the geo- 

 graphical distribution of animals upon the 

 surface of our globe, but this is a point upon 

 which I am not yet prepared to give full 

 and satisfactory evidence. So much for 

 the views referring to embryology in its 

 bearing upon zoological classification." 



And again on p. 27: 



" However, another step had to be made 

 to show a real agreement between the 

 earlier types of animals and the gradual 

 development of the animal kingdom, which 

 has been the last progress in our science of 

 fossils : namely, to show that these earlier 

 types are embryonic in their character — 

 that is to say, that they are not only lower 

 in their structure when compared with the 

 animals now living upon the surface of our 

 globe, but that they actually correspond to 

 the changes which embryos of the same 

 classes undergo during their growth. This 

 was first discovered among fishes, which I 

 have shown to present, in their earlier 

 types, characters which agree in many re- 

 spects with the changes which young fishes 

 undergo within the egg. Without entering 

 into all the details of these researches, I 

 will conclude by saying it can now be 

 generally maintained that earlier animals 

 correspond not only to lower types of their 

 respective classes, but that their chief pe- 

 culiarities have reference to the modifica- 

 tions which are successively introduced 

 during the embryonic life of their corre- 

 sponding representatives in the present cre- 

 ation. To carry out these results in detail 

 must now be, for years to come, the task of 

 paleontological investigations." 



V, 



