TRANSACTIONS OF THE SECTIONS. 127 



ctenophorous medusa a radiated animal. Similar instances may be taken from the 

 higher divisions of the animal kingdom ; as they are known to all who are familiar 

 ■with our zoological system, I shoidd go too far if I were to specify what a little 

 attention paid to different orders of animals will tell in a moment. The simple 

 result of carefully looking through the established classes and orders of animals, is 

 that there is only a relative weight to be laid upon the different groups of zoolo- 

 gical characters. It depends entirely upon the whole typical organization, and on 

 the correlation of parts as modified by that type. This correlation of parts, which 

 allows us to draw a conclusion from the nature of one organ as to the nature of 

 another, must naturally be changed by the physiological dignity of an organ, which 

 in different types is not always the same ; and it will become uncertain whenever 

 the characters which we call specific are becoming indistinct themselves. 



I thought it necessary to state first in few words, that there is a difference in the 

 value of zoological characters according to different classes, and I am of opinion 

 that the progress of zoology as science depends mainly on the determination of 

 this value in a sharper manner than it has been stated. I published some years 

 ago some general remarks on this subject in a small pamphlet which will scarcely 

 have reached England. Since then my opinion has become still stronger, as I saw 

 that the progress, which zoology owes of late years especially to some eminent 

 British naturalists, was chiefly dependent on the circumstance that the point men- 

 tioned was, with or without purpose, taken into consideration. 



The structure of animal bodies shows three different relations of complexity ; com- 

 mon to all three are these two points ; first, that a structure, at first simple, becomes 

 more and more diversified ; secondly, that all the differences which appear one after 

 the other make their appearance on a basis fundamentally equal and in itself not 

 changing. They differ according to the difference of this substratum. In one case 

 there is one and the same body changing and becoming more and more complex ; 

 in the second case different members of one great fundamental type of organization 

 constitute a series of forms, some less, some more diversified ; in the third case the 

 very types themselves are to be regarded as members of one great series, showing 

 less* and greater complexity. The practice of scientific inquiry has severed these 

 three different points of view into three different branches of science. The first is 

 the history of development, which may just as well be called the comparative 

 anatomy of the individual; the second is the comparative anatomy of the different 

 types ; the third is the general morphology of the animal kingdom. These are the 

 three different bearings which animals generally present to the zoologist with regard 

 to their structure. Now we must ask, what use can we make of them, and of the 

 first-mentioned especially P As the zoologist has nothing before him but individuals, 

 it is no wonder that the comparative anatomy of these will throw much light on 

 their nature, their life, and their morphology. As long as it is kept in mind that 

 all the facts of the history of development have relation to the individual, and to 

 nothing else, so long nobody will object to the manner of inquiring, which is quite 

 properly called the genetic method. 



All our zoological classification, however, tends toward the establishment of 

 larger groups and types, and here comparative anatomy has its place. It is very 

 significant, that in the Cuvierian system, which we all follow, its later alterations 

 being quite irrelevant to the grand truths upon which it is founded, there is no 

 use whatever made of the history of development, not even in one instance. It 

 has been said that the emendations of this system, and the whole progress of 

 systematic zoology, depend, if not chiefly, yet for a great part, on the employment 

 of the genetic method. On this I may be allowed to make the following remarks. 

 As comparative anatomy rests entirely on the knowledge of the structure of indivi- 

 duals, everything which throws light on the individual will also throw light oh 

 comparative anatomy. But with regard to systematic zoology, we have not to 

 deal with larval forms and immature individuals, but only with such as are able 

 to propagate their individual, or if you like it better, specific form. We cannot, 

 of course, put aside all embryological data in our systematic endeavours. How- 

 ever, there is great danger in overrating the help they give us. A system based 

 on anatomy alone is an artificial one, however true it may be ; but its value is 

 always great, and the more attention is paid to the physiological and biological 

 bearings of structural facts, the greater will this value be. A classification of 



