436 heviews. 



Again and again throughout the course of the same chapter Pro- 

 fessor Agassiz insists strongly against the evils which must accrue to 

 systematic zoology from a confusion between the fundamental dif- 

 ferences in plan of structure observable amongst animals, and those 

 minor differences having reference to the various modes in which the 

 execution of the same plan may be carried out. But of what avail 

 is it to enunciate this general proposition, the truth of which all 

 intelligent naturalists, familiar with the principles of Von Baer. 

 have long been accustomed to admit, if, at the same time, he fail to 

 perceive the true import of those great anatomical features, which 

 distinguish the group of Coelenterata ? If these be not enough to 

 constitute a distinct plan of structure, and not merely a variation in 

 the mode of execution of some other plan, it may be asked what 

 amount of morphological peculiarity can be considered sufficient for 

 this purpose ? Or do sub-kingdoms exist only in the imaginations of 

 Cuvier and his successors, and ought the entire animal kingdom, as 

 in the time of Linnreus, to be resolved at once into classes ? In thus 

 refusing to acknowledge so natural an assemblage as the Coelenterata, 

 Professor Agassiz, as he himself with characteristic candour admits, 

 entertains views adverse to those of many G-erman, and, we may add, 

 of many English naturalists. Even Professor Milne Edwards, who, 

 occupying as he does, the distinguished position of successor to 

 Cuvier, might well be excused were he to cherish a prejudiced and 

 too literal adherence to the system of his great predecessor, though 

 he does not elevate the Coelenterata to the rank of a sub-kingdom, 

 goes so far as to regard them, with their several classes, on a par 

 with the single class of Echinoderms, the two groups, being consti- 

 tuted, in his recent arrangement, equal and primary divisions of the 

 I£adiata. # 



But it should not be forgotten that the definition of the sub- 

 kingdom Coelenterata includes another clause in addition to that 

 specified by Erey and Leuckart. It is now many years since the 

 body- sub stance in all these animals has been shown by Professor 

 Huxley, (who, we believe, first drew attention to the fact), to be re- 

 solvable into two foundation membranes, an outer and an inner, for 

 which he proposed the names of ectoderm and endoderm. The subse- 

 quent researches of many naturalists have tended more and more to 

 confirm this generalization. And if, by the light of our present 

 knowledge, we carefully peruse the works of those older writers who 

 acquired by patient investigation the useful faculties of seeing only 

 what they ought to have seen and recording only what they saw, we 

 shall not fail to perceive that they too were not without their own 

 presentiment of a truth which appears to us of such importance. 

 In their thread- cells, also, the Coelenterata, exhibit another structural 

 peculiarity, not unworthy of consideration. 



To all" this, however, Professor Agassiz replies that there is a 



* Histoire Nnturelle des Coralliaircs, Tom. I., 857, pp. 3-4. 



