ON THE ORIGIN OF GENERA. 77 



different positions at tlie same or different periods of the earth's 

 history.* 



Prof. Marcel de Serres proposed the theory of repressions of 

 develojDment to account for the existence of the lower groups of 

 animals as 7iow existing^ an error easily exposed, as has been done 

 by Lereboullet in his yarious important embryological writings. 

 But little obseryation is sufficient to prove that a mammal is not 

 a shark where it has five gill-arches or aorta-bows, nor a batrachian 

 where it has three, or a reptile where it has the two aorta-roots. 

 This has been already sufficiently pointed out by von Baer, who 

 says there is " keine Eede " of such a theory as was afterward 

 proposed by de Serres. Thus are true the rules propounded by 

 this author, f 3. ^^Each embryo of a given animal type, instead 

 of passing through the other given animal found, diverges still 

 more from it." 4. ^^ In the basis, therefore, the embryo of a 

 higher animal type is never identical with an inferior type, but 

 with the embryo only of the latter." 



I think that I have already made some progress in proving 

 that the near or true generic relationship is one of absolute devel- 

 opmental repression or advance. Paleontology shows that fami- 

 lies and orders, as now existing, were preceded in time by groups 

 which are synthetic or comprehensive, combining the common 

 characters of modern generic series. This process of synthesis 

 must, it is obvious, if continued, result in the near approximation 

 of the single representatives of the now numerous and diverse 

 groups. There is every reason to believe that a backward view 

 through time will show this to have prevailed throughout the 



* Some naturalists seem to imagine that the demonstration of the existence of 

 intermediate types is only necessary to establish a developmental hypothesis. Thus 

 Dr. Dohrn (" Ann. Magaz. N. Hist.," 1868), writing of his discovery of that most 

 interesting genus, Eugereon, which combines characters of Neuroptera with those of 

 Hemiptera, does not hesitate to say that it proves the truth of Darwin's theory. 

 Now, it appears to me that a demonstration of the existence of a regularly graduated 

 succession of types, from the monad to man, would be only the minor of a syllogism 

 without its major, in evidence for development, so long as the proof of transition 

 of one step into another is wanting ; and the idea that such a discovery could estab- 

 lish a developmental theory is entirely unfounded. Indeed, the reasoning in which 

 some indulge— if we dare so call the spurious article— based on this premise alone, 

 is unworthy of science. The successional relation of types, though a most important 

 element in our argument, has been long known to many who give no sanction to 

 the idea of development. 



f " Entwickclungsgeschichte," p. 224. 



