^2 REMARKS ON THE PRINCIPLES OF 



their inferiority of grade, though they, "undouhtedly, occupy the 

 lowest grade in the animal kingdom ; and, I think, on reconsideration. 

 Dr. Dawson will find that, whilst the name Protozoa is proposed for an 

 assemblage of low forms^of animal life, possessing certain remarkable 

 common characters, those who have adopted it have carefully excluded 

 other almost equally low forms, which display the characteristics of 

 any of the other sub-kingdoms. If the principal characters be 

 negative, which is very apt to be the case with the lowest division of 

 any great group, as being what is left when the others are withdrawn, 

 and known by the absence of all their distinctive peculiarities, yet, 

 if the remnant of the animal kingdom which cannot, with any 

 appearance of propriety, be referred to any of the four recognized 

 plans of structure, consists of beings considerably resembling each 

 other in substance, vital functions, and the means by which these are 

 performed, so far as they are known, a tolerably secure foundation is 

 laid for the fifth sub -kingdom ; and, if all its members, as in the case 

 of Radiata, may be referred to three distinct classes, (Porifera, 

 Rhizopoda, Ciliata,) this analogy with the nearest sub-kingdom 

 confirms the argument. Agassiz is the most formidable opponent of 

 the separation of Protozoa, and every opinion of his deserves to be 

 carefully weighed, and treated with respect ; but, in the present case, 

 we find him obliged, in opposition to the views of all who have most 

 carefully studied them, to send back the Sponges to the vegetable 

 kingdom, and, in defiance of recent exact observation, to return to 

 the old plan of treating Foraminifera as low forms of Cephalopods ; 

 besides that, because his own acute observation had proved some 

 supposed Ciliata to be embryonic forms of higher animals, he, too 

 hastily, concludes that all the Ciliata will probably admit of the same 

 explanation, although of some of them the whole life-history may 

 be said to be ascertained. I cannot but think that, in this case, a 

 preconceived opinion established in his mind, and, having a fixed 

 place in his general system, has prevented this great naturalist from 

 perceiving the truth with his usual sagacity. I, at least, find my 

 convictions strongly opposed to this opinion of Dr. Dawson, high as 

 is the authority by which he might support it. 



In the section on the general nature of the animal, the distinctions 

 between the animal and vegetable kingdom are by no means free from 

 objection. The first is merely verbal, since eggs and seeds are 

 essentially of the same nature, and cannot always be distinguishe 



