hitrodudion to Animal Morphology. 25 



sorbing oxygen, and evolving carbonic acid. Muscle 

 and nerve exist only in them, as are the more complex 

 forms of connective tissue. Haeckel proposes to make 

 a third kingdom. Protista,* of a series of living beings 

 intermediate between plants and animals. But most 

 of these, though not falling in rigidly with the defi- 

 nition of either, have recognizable affinities pointing 

 to one group or the other, and as the limits of every 

 class are arbitrary, it is easier to draw one line of 

 demarcation than two : hence I have not adopted this 

 arrangement. 



The animal kingdom, as it presents itself to us, is a 

 vast assemblage of individual forms. Individual may 

 be used as a physiological or as a morphological 

 term; in the former sense it means a single form 

 enjoying independent life for a longer or shorter time, 

 in the latter, a single form which is in itself an in- 

 divisible whole, whose parts are integral. Sometimes 

 the morphological individuality is a matter of dif- 

 ference of opinion, as among Sponges. Dr. Carpenter's 

 definition of an individual (the total product of a single 

 fertilized ovum) is inapplicable to most of the Protozoa 

 and confusing in discontinuous colonies, but yet with 

 a more perfect knowledge, doubtless it will be 

 found to be nearest to the truth. A morphological 



* This kingdom, if recognised, would contain nine classes : — 

 I. Monera, composed of cytodes ; 2. Protoplasta of cells, divided into 

 Gymnamoebse, Lepamcebse, and Gregarinse (all these have animal affinities) ; 

 3. Diatomaceae, with sihceous shells, generally regarded as unicellular 

 Algse ; 4. FlageUata, a mixed group, some probably vegetal, others cer- 

 tainly animal ; 5. Myxomycetae, a most problematical group, with affinities 

 to Fungi, but even stronger relations to Protozoa ; 6. Labyrinthulea, 

 animals ; 7. Phycochromacea ; 8. Fungi, both usually regarded as vegetal ; 

 9. Radiolaria. 



