126 THE IDEAL TYPES OF THE 



than the so-called bony-fishes ; their brain is of a higher order ; 

 their circulatory and respiratory system is also superior ; and the 

 organs of reproduction are not only higher, but approach closely 

 to those of reptiles. So we see that the bony nature of the ver- 

 tebrrc is not the essential characteristic of Vertebrates ; it is the 

 presence of some longitudinal mass, either bone, or gristle, or 

 interlaced fibres, or a mere jelly-like string, as in Amphioxus, (fig. 



ns v l ov lv l g b Iv br h* h 8 A 2 n?- 1 o no 



65, v, i; 1 ,) which is intended to separate the main nervous cord 

 from the rest of the organs ; it is the presence of this ideal, as I 

 may call it, that constitutes the characteristic of Vertebrates. 

 In other words, it is an ideal axis materialized. 



From this you may judge that in considering typical forms of 

 life, it is the relation and not the nature of a substance which is 

 to be taken into account. Relation should be the ruling standard. 



Accordingly, therefore, we see in the Protozoa, (figs. 55, 56,) the 



Fig. 65. Amphioxu/t lanceolatus. A diagramic figure of the Lancelet. Nat- 

 ural size. % /", the head ; v, u', the notochord, or vertebral column ; ws, the sheath 

 of i>, v l ; fte, the buccal cirrhi ; _/, the buccal ring at the entrance to the mouth ; 

 I, IT, oval bodies projecting freely into the buccal cavity ; 1 , entrance to the 

 throat or branchial cavity ; </, posterior end of the same, and entrance to the in- 

 testine proper (i) ; fto, the lateral branchial openings ; i 1 , posterior end of /; Iv, 

 h' 1 , appendage to i, opening into it at h* ; /*, the heart ; A 1 , /;'*, the anterior blood- 

 vessels; /; 3 , branches from A 4 , supplying I, II; A 4 , 7< 6 , the dorsal artery; h 5 , the 

 abdominal vessel ; ft, the upper, and ft 1 , the lower point of junction of the 

 branchial vessels (ft?-) with the dorsal (A 4 , A 6 ) and ventral (A 1 , k*) vessels ; etc, 

 abdominal cavity ; ap, abdominal pore ; nr l , the anterior, and nr, the posterior 

 end of the main nerve or spinal marrow ; ns, sheath of wr, nr 1 ; o, the eye ; , 

 the olfactory nerve ; nv, the facial nerves; ov, the reproductive organ. From 

 Owen. 



