6 



PROF. AGASSIZ ? S 



facts could be acquired. The knowledge of a few 

 fish, enabled him to compare the whole class of 

 fishes with reptiles ; a knowledge of a few rep- 

 tiles, enabled him to institute extensive compari- 

 sons between reptiles and birds ; and again, be- 

 tween these and mammalia ; and to find that all 

 these animals agree in certain respects. And how- 

 ever many have been examined since, and three 

 or four times more have been examined than the 

 number which Cuvier had known when he laid 

 out his classification however many have been 

 studied since, they have all been found to agree in 

 these essential particulars. So that it is now plain, 

 that structure ia the principle upon which animals 

 can be most satisfactorily classified. And as I shall 

 often have occasion to refer to this classification 

 let me at once, in a few words, indicate which great 

 divisions Cuvier introduced into his animal king- 

 dom. 



All the animals which I have mentioned, Fishes, 

 Reptiles, Birds, and Mammalia, are combined to- 

 gether, because they have a series of backbones, 

 called vertebrae, by anatomists \ and hence the 

 name of vertebrated animals. They agree ia the 

 general structure of their brain ; they agree in the 

 general arrangement of the fleshy parts, and in 

 the general arrangement of the organs of life 

 as of the organs of respiration, the heart, the ali- 

 mentary canal, and so on. 



Another group t which was established on the same 

 principle, is that to which we may refer worms, 

 insects, crabs and lobsters all animals whose bo- 

 dies are divided into a series of moveable rings, 

 joints, which surround the body and enclose 

 the soft parts ; and which are provided with move- 

 able legs, and in some, even in addition to these 

 legs, also with wings. All these animals have a 

 most remarkable arrangement of the nervous sys- 

 tem ; there being a series of swellings of nervous 

 substance placed, one in each of the rings, and 

 connected together by double threads ; so that the 

 nervous system is all contained in one cavity, not 

 only the general arangement of parts,but this most 

 important organ of life is also different from that of 

 vertebrates. 



The next great group is that of Mollusca, contain- 

 ing cuttle-fish, snails, slugs, clams, and oysters, 

 all those animals which we generally call shell-fish 

 those which are provided with hard structures 

 the body being soft and generally surrounded by 

 a great quantity of mueosity j the nervous system 

 consisting simply of a circle surrounding the ali- 

 mentary tube, with a swelling above the intestine, 

 and another below, from which all the nervous 



threads arise, which are diffused into all parts of 

 the body. 



In these three groups of the animal kingdom, 

 all parts are in pairs, placed on two sides of the 

 longitudinal axis. In all of these there is an ante- 

 rior and posterior part ; two sides, a right side and 

 * left side , and they have a back part and a lower 

 part ; they are, in fact, symmetrical. 



But there is another group, in whicS there is a 

 different arrangement. The mouth is in the cen- 

 tre of a circular bodv j and from this mouth, the 

 organs are placed like rays, diverging in all direc 

 tions. Here we have no right, and no left side, no- 

 anterior and no posterior extremity. The body i 

 star-shaped -, and the nervous system has the same 

 general structure, consisting of an horizontal ring 

 around the entrance of the alimentary tube, and 

 has no longer an upper and a lower swelling, as in 

 Mollasca. 



There have been a few modifications made in the 

 details of this arrangement as proposed by Cuvier. 

 Some of the animals placed among the mollasca, 

 were found to belong to the group of articulata. 

 Barnacles are one of this group ; a very remarkable 

 family, from the numerous shells around the body. 

 Without knowing certainly, he had placed thern 

 among the mollusca; but on examination, it wa& 

 found that their nervous system consisted of swel- 

 lings, and that their bodies were divided into joints 

 and an additional evidence was obtained from a 

 knowledge of their young, which were found to 

 resemble, in the earlier stage, much more the crus- 

 tacea than the mollusca ;. and indeed, that they 

 were Crustacea, and assumed this covering only ak 

 a later epoch. 



However important these anatomical researches 

 have been,it is nevertheless my belief that in this line 

 of investigation we have gained all the important 

 information that we can gain ; and that we have to 

 run new tracks in order to improve our natural 

 method, that we must even give up this funda- 

 mental principle, as the ruling principle, if we will 

 make further advance in this science. And my 

 reason is this : The minute investigations which are 

 now making in the anatomy of animals, are bring- 

 ing forward such differences between them, that 

 we have no principle by which we can appreciate 

 their value, And if we consider every difference in 

 structure as sufficient to separate animals, the time 

 would come when we should form as many groups 

 as many divisions as there would be smaller 

 groups in the animal kingdom, as it can be shown 

 that even genera differ anatomically among them- 

 selves. 



If I am not entirely mistaken, these new investi- 

 gations, this new information, must be derived 

 from embryological data. It is to the study of 

 young animals it is to the investigation of the 

 formation of the germ within the egg, that we 

 must appeal for a ruling principle to ascertain the 

 real, natural position of the subdivisions of the mi- 

 nor groups in the animal kingdom. I acknowledge 

 that the great divisions will always stand on the an- 

 atomical structure. But the subdivisions of the 

 classes cannot rest upon anatomical investigation j 

 and if I do not fail in my endeavors,! hope to show 

 it to you satisfactorily. This new step is a natural 

 consequence of the natural progress and state of 

 our science. 

 Investigations have recently been carried on, 



