12 



PROF. AGASSIZ'S 



LECTURE II. 



The object of my first lecture was, to show that 

 after Comparative Anatomy had illustrated the 

 general relations of the animals throughout the 

 animal kingdom, it was possible to ascertain more 

 closely the nearer affinities of the different minor 

 groups, by tracing the relations which exist be- 

 tween full grown animals and the changes which 

 animals of the same family undergo during their 

 earlier stages of growth, from their first formation, 

 in the egg to the epoch when they are full grown. 

 In one instance, I think it has been possible for 

 me to show that the various forms which we ob- 

 serve in the class of reptiles, in that order of rep- 

 tiles which naturalists call Batracbians, really cor- 

 respond in their general character, though not in 

 the particular features of their proportions, to 

 those which the higher species of Batrachians 

 present up to the time when they have assumed 

 their higher form. This result shows that the 

 principle exists ; though its application in the dif- 

 ferent classes of the animal kingdom is at present 

 not possible in all its details. 



But this result gives also evidence of another 

 important view ; that is, that there is really a plan 

 in the animal kingdom ; a plan which can be read 

 without any part of the view arising from us, but 

 being taken from nature. We read there the do- 

 ings of an Intelligence which created those things ; 

 and we can read even more than that, in this plan. 

 On dwelling upon another fact, in my Wednesday 

 Afternoon lecture, I showed that this plan is not 

 carried out in one locality, in a few types merely,; 

 but that it is worked out all over the surface of our 

 globe; and thai, therefore, the result of this in- 

 vestigation shows the Omnipresence of the Crea 

 tor in his creation. 



It becomes now my duty to enter upon a special 

 illustration of the various classes of the animal 

 kingdom, in order to trace, if possible, similar re- 

 lations between them. 



I shall begin with the great group of radiata, the 

 lowest in the animal kingdom. My reason for do- 

 ing, so is, that the animals belonging to this type 

 are the simplest; and perhaps it will be easier to 

 show here how the egg, with its simple elements, 

 can undergo such changes as to give rise to the 

 formation of an animal; and the changes not be- 

 ing so extensive as they are in higher animals, it 

 will be more readily understood how they are 

 brought about. 



The type of radiated animals is divided into 

 three classes: the polypi, or polyps; the jelly- 

 fishes, or medusas; and the echinoderms, or star- 

 fishes and sea-urchins. These three classes differ 

 in their general structure, and their differences 



have been made out by anatomical investigations. 

 They have general relations to each other, by which 

 they belong to the type to the great group of 

 radiata. Owing to their simpler structure, the po- 

 lypi stand lowest ; next come the medusae or jelly- 

 ashes ; and among radiata we place the echino* 

 lerms highest. 



I shall begin with the echinoderms though per- 

 haps the polypi, from their simpler structure, may 

 answer best the first purpose to which I alludedj 

 and be more easily understood, But there is an 

 objection to my taking up polypi first; it is the 

 fact that naturalists have not agreed as to the sub* 

 division of polypi into families, from the fact that 

 their structure being so simple, it is difficult to 

 estimate the value of the differences which they 

 present; and therefore, these differences have 

 not brought to light a clear gradation of the fami- 

 lies. And perhaps there is another difficulty with, 

 them to overcome the fact that individual life is 

 not so distinct among polypi; that several individ- 

 uals remain combined together to lead a common 

 life ; and therefore, we should have to allude to 

 increased difficulties in the estimation of these 

 beings, when investigating the mode by which in* 

 dividual life is established, and by which individu- 

 als grow. Those difficulties will be easier under- 

 stood after we have traced the growth of animals 

 which are really individuals in the proper meaning 

 of the word; that is to say, which grow isolated 

 which are detached from the parent early in life, 

 and grow separate. 



The Medusae would perhaps answer next; but 

 so singular phenomena have been observed among 

 them that I fear to allude to them at once. We 

 observe, namely among the Medusae, the singular 

 circumstance of alternate generations ; that is, of a 

 progeny which do not resemble the parent of a 

 second generation which differs from the first, a 

 second generation which returns to the form of the 

 grandparents; and so on successively. And this 

 singular order of succession of individuals of differ- 

 ent aspects, makes it difficult to understand their 

 different analogies to understand the differences 

 by which the two generations differ. Therefore I 

 shall begin with the highest class with the Echi- 

 noderms where we have, in the successive gener^ 

 ations, truly independent individuals, arising from 

 parents similar to their progeny. Moreover, the 

 Echinoderms have been extensively studied , they 

 have been the object of monographic investiga- 

 tions; their genera are well characterised and nat- 

 urally circumscribed. A great many of these have 

 been found in a fossil state, and these fossil remains 

 will compare with the living types. Such differen- 



