24 REMARKS ON THE PRINCIPLES OF 



thus far agreeing with Dr. Dawson, and valuing highly his testimony 

 in favour of a great principle, I cannot agree with him as to the actua^ 

 number of these distinct tendencies which I am compelled to estimate 

 as five instead of four. In regard to the primary division of the 

 animal kingdom into sub-kingdoms or branches, after granting the 

 excellence of the four established by Cuvier, and fully agreeing in Dr. 

 Dawson's judgment respecting Coelenterata, Molluscoida, and Annu- 

 loida, I find myself compelled to accept the additional group of Pro- 

 tozoa, because there are many living beings with structural peculiari- 

 ties adapted to their designed mode of existence which have no rela- 

 tion in their plan of structure to any of the other four sub-kingdoms, 

 and which, notwithstanding remarkable differences among themselves, 

 agree together in the nature of their substance and the simplicity of 

 the means by which the functions of life are carried on. The very 

 illustration drawn from architecture which Dr. Dawson has used to 

 justify his rejection of Protozoa, seems to me to shew the necessity of 

 admitting it as a branch, for surely if I were required to give an 

 account of all human habitations arranged according to their nature, I 

 must not only notice the distinct styles of the higher architecture, but the 

 rudest huts and hovels and the simplest tents must also be described, 

 and their few common features with the absence of the characteristics 

 of the higher styles would bring them together as a class. So when I 

 attempt as a zoologist to give some account of the whole animal king- 

 dom, I must not entirely neglect any really existing group, and if I 

 find many forms which can with no appearance of reason be referred 

 to any of the former plans with which we first become acquainted, 

 although their extreme simplicity must make their characters chiefly 

 negative, I must place them together as a fifth sub-division since 

 there is no other course which would not render the characters of the 

 others nugatory. To me, again, it is an argument in favour of re- 

 ceiving the Protozoa, that, notwithstanding their extreme simplicity 

 and minuteness, they naturally fall under three distinct classes : 

 Rhizopoda, Porifera, and Ciliata, which seem to include them all 

 the very number of classes corresponding with the next lowest sub- 

 kingdom, Radiata and differing from the others only by the absence, 

 of the two higher tendencies which are not specially manifested in 

 these low forms of living beings. 



If we can establish five great branches of the animal kingdom thg 

 presumption, according to principles admitted and well supported by 



