ZOOLOGY. 



tion (Fig. 333); they are the most imperfect of all the 

 ordinary vertebrata. Their skeleton is sometimes mem- 

 branous, as in the amocetes or river lampreys, and is always 

 less complex than in other fishes; 

 their nervous system is but little 

 developed, and the gills have the 

 form of small bags. The lampreys 

 (Fig. 334) constitute the principal 

 type of this group. 



506. A very singular animal, 

 evidently belonging to the vertebrata, 

 but deficient in many of their cha- 

 racters, has lately attracted some 

 attention. It is called the amphi- 

 oxus, and is a small marine animal, 

 sufficiently like a fish, but which has neither vertebrae 

 properly so called, nor heart, nor red blood, nor a distinct 

 brain. Its skeleton is represented by a cartilaginous stalk, 

 resembling the cartilaginous cord preceding the formation of 



Fig. 333. Mouth of the 

 Lamprey. 



Fig. 334. The Lamprey. 



the vertebral column in the embryo of the ordinary verte- 

 brata ; the cerebro- spinal axis occupies its usual place, but 

 presents anteriorly no enlargement which may be compared 

 to a brain; the circulation is accomplished by means of 

 vessels whose walls are contractile, and the walls of the 

 pharyngeal cavity take the place of a respiratory apparatus. 

 Most zoologists arrange this degraded vertebral animal in the 

 class fishes; but it seems evident to us, that in a natural 

 classification the amphioxus ought to occupy a particular 

 division. 



[It formed no part of the plan of the author's excel- 

 lent work to follow out any of the great views which the in- 

 troduction of the transcendental anatomy into science has 

 forced on the consideration of all observers, and I have there- 

 fore not deemed it necessary to add largely to the few hints 

 given by the author himself. As in a passage or two of the pre- 

 ceding portions of the work the author has glanced at a sub- 

 ject of great interest, namely, the distinctness of species and 



