214 PROCEEDINGS OP THE AMERICAN ACADEMY. 



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 siirface 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 respects with the changes which young fishes under- 

 go within the egg. Without entering into all the details of these re- 

 searches, I will conclude by saying it can now be generally maintained 

 that earlier animals correspond not only to lower types of their respect- 

 ive classes, but that their chief peculiarities have reference to the modifi- 

 cations which are successively introduced during the embryonic life of 

 their corresponding representatives in the present creation. To carry 

 out these results in detail must now be, for years to come, the task of 

 paleontological investigations." * 



* Prof. George Baur of Chicago University has, since tlie above was written, 

 called my attention to Carl Vogt's " Embryologie des Salmones," publisiied un- 

 der the general title of " Poissons d' Eau Douce," par L. Agassiz, Neuchatel, 1842. 

 I take the following quotations from his pages. 



Vogt says, on the second page of the Preface, after stating that Louis Agassiz 

 had handed this part of the work over to him: "En me confiant une tache aussi 

 honorable, mon ce'lebre ami n'est cependant point reste ctranger a mes recherches. 

 Nous avons discute' ensemble les faits cajiitaux, a mesure que I'observation me 

 les revclait; souvent meme nous les avons examines de nouveau en commun, et 

 lorsque j'eus re'dige mon travail, c'est encore lui qui a bien voulu le revoir." 



Again, on pages 256, 257 : — 



" Depuis longtemps on a discute duns des sens tres-divers la question de I'analogie 

 entre les phases du deveJoppement des animaux vivants maintenant et les changements qui 

 sent su7-i-enus dans Vordre de succession des especes fossiles ; mais faute de renseigne- 

 mens precis sur Ton ou I'autre des cotes de la question, ces generalisations sont 

 reste'es dans un vague tres-facheux pour les vrais progres de la science. Sans en- 

 trer ici dans des considerations hasardees, sans aborder le domaine encore trop peu 

 cultive de la plus grande analogic qu'ofFrent entre elles les diffcrentes parties du 

 corps des poissons fossiles les plus anciens et que Ton pourrait paralleliser avec 

 riiomogeneite des tissus primitifs de I'embryon, je me bornerai a faire ressortir 

 quelques points qui ne sauraient plus etre conteste's et qui, je I'espere, feront 

 faire de nouvelles recherches sur I'ensemble de la question." 



Vogt concludes, on page 260, as follows : — 



"On pourra done dire a I'avenir, en restant rigoureusement dans les limites de 

 I'observation, qu'Ii certains c'gards, les especes fossiles d'une classe parcourent dans 

 leur succession historique des metamorphoses semblables a celle que subissent les 

 embryons en se developpant ; ou vice-versa, que les embryons des animaux de 

 notre c'poque passent, dans les differentes epoques de leur dcveloppemeut par des 



