268 



PROCEEDINGS OF THE ACADEMY OF 



donotus at a certain period, that it is far in advance of that of the mammal at 

 the same stage. Here, says the objector, is a case where their parallelisms do 

 not coincide; the mammal is really similar to a younger stage of the Reptile, 



But, in fact, the size of the eye is but a generic or family character ; if the 

 development of the lemur had been compared with the snake, ihe mammal 

 would have liccn found to be in advance ; if the mole, much farther behind. 

 If the snake selected were the purblind Atractaspis, almost any mammal would 

 have been in advance ; if, on the other hand, the great eyed Dipsas, but few 

 mammalia would have been parallel to it. 



In a word, to find exact paralUlism it is necessary to examine the closest 

 allies. 



It is also of first importance to distinguish between the ez/s^e?ice of generic or 

 higher characters, and their condition under various circumstances of individual 

 life. If a foetal or larval character be conserved through the adult life of a 

 type, it will be of course adapted to the functions of mature age. Thus the 

 undeveloped character of the horns of the genus of deer, Rusa, are not accom- 

 jianied with the marks of individual youth of the corresponding stage of Cer- 

 vus; its individuals are fully grown and funclivnal/i/ ^eviect. The species of 

 Hyla are not small and incapable of self preservation and reproduction, as is 

 the corresponding stage of Trachycephalus ; they are functionally developed. 

 The student need not he surprised, then, if, when identity or exact parallelism 

 is asserted, he finds some diflerences dependent on age and adaptation, for if he 

 be an anatomist he need not be informed that a morphological relation consti- 

 ttites types what they are, not a physiological. 



II. 0/ retardation and accelerati&fi in generic characters. 

 First. Of adult metamorphosis. 



The question has necessarily arisen — have these remarkable relations between 

 genera resulted from an arrangement of distinct generations according to a 

 permanent scale of harmony, or have the same genetic series of individuals 

 been made to assume the different positions, at the same or different periods of 

 the earth's history.* 



Prof. Marcelde Serres proposed the theory of repressions of development to 

 account for the existence of the lower groups of animals as now existivg, an 

 error easily exposed, as has been done by Lereboullet in his various important 

 embr3'ological writings. But little observation is sufficient to prove that a 

 mammal is not a shark where it has five gill arches or aorta bows, nor a batra- 

 chian 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 

 " Kein Rede," of such a theory as was afterwards proposed by de Serres. 

 Thus are true the rules propounded by this author. f 3. "Each embryo of a 

 given animal tyi)e, 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 em- 

 bryo only of the latter " 



* Some naturalists .se^im to imagine that tlie demonstration of tlie existence of interme- 

 diate types IS only necessary to establish a developmental hypothesis. Thus Dr. Dohrii 

 (Ann. IVIagaz. N. Hist., 1808), writing of his discovery of that most interestins; genus Euge- 

 reon, vviiieh combines (diaraeters of Neuroptera with those of Hemiptera, dues not iiesi- 

 tate to say that it proves tlie truth of Darwin's theory. Now it appear.s to me that a dem- 

 onstration of the existence of a regularly graduated succession of tj'pes from the monad to 

 man, would be only tlie m nor of a syllogism without its major, in evidence for develop- 

 ment, so long as tlie proof of transition of one i^tep into another is wanting; and the idea 

 that such H discovery could establisli a developmental theory is entia'ely unfounded. 

 Indeed tlie 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 developinent. 



t Entwickelungsgeschichte, 224. 



[Oct. 



