226 THE ORGANIZATION 



CHAPTER XIII. 



VERTEBRATA. 



As I have already and at considerable length (p. 124) dis- 

 cussed the characteristic features of Vertebrata, I need not 

 enter into any further details in regard to their relation to the 

 typical form, but simply ask you to make the comparison for 

 yourselves between the ideal figures (figs. 63, 64) of this type 

 and the diagrams of the actual organization which I am about 

 to describe. I hardly need to say that you will not find an 

 identity in the details, but a perfect accordance in the relative 

 position of the four systems of organs, namely, the nervous, ver- 

 tebral, digestive, and circulatory. Among the lower groups of 

 Vertebrata these systems are more clearly demonstrable in a 

 diagram than among the higher ranks, as you may see by a 

 comparison of this diagramic illustration of a Fish (fig. 133) 



ns v 1 ov lv l a b Iv br h* A 3 A 2 nr 1 o nv 



Fig. 133. Ampliioxus lanceolatus. A diagramic figure of the Lancelet. Nat- 

 ural size. f, the head ; v, v 1 , the notochord, or vertebral column ; vs, the sheath 

 of r, i- 1 ; be, the buccal cirrhi ; /, the buccal ring at the entrance to the mouth ; 

 I, II, oval bodies projecting freely into the buccal cavity ; bo, the lateral bran- 

 chial openings ; gr 1 , entrance to the throat or branchial cavity ; g, posterior end 

 of the latter, and entrance to the intestine proper (i) ; fl, posterior end of i ; Iv, 

 lv l , appendage to i, opening into it at lv^ ; h, the heart ; h 1 , 1ft, the anterior blood- 

 vessels ; Ifl, recurrent branches of those, from &*, which supply I, II ; A 1 , A 6 , the 



