THE AMPHIOXUS. 199 



of all the Vertebrate animals known to us. This exceedingly 

 interesting and important animal, which throws a surprising 

 light upon the older roots of our pedigree, is evidently the 

 last of the Mohicans — the last surviving representative of a 

 lower class of Vertebrate animals, very rich in forms, and 

 very highly developed during the primordial period, but 

 which unfortunately could leave no fossil remains on account 

 of the absence of all solid skeleton. The Lancelet still 

 lives widely distributed in different seas; for instance, 

 in the Baltic, North Sea, and Mediterranean, where it 

 generally lies buried in the sand on flat shores. The body, 

 as the name indicates, has the form of a narrow lanceolate 

 leaf, pointed at both extremities. When full grown it is 

 about two inches long, of a white colour and semi-trans- 

 parent. Externally, the little lanceolate animal is so little 

 like a vertebrate animal that Pallas, who first discovered it, 

 regarded it as an imperfect naked snail. It has no legs, 

 and neither head, skull, nor brain. Externally, the fore end 

 of the body can be distinguished from the hinder end only 

 by the open mouth. But still the Amphioxus in its internal 

 structure possesses those most important features, which 

 distinguish all Vertebrate animals from all Invertebrate 

 animals, namely, the spinal rod and spinal marrow. The 

 spinal rod (Chorda dorsalis) is a straight, cylindrical, 

 cartilaginous staff, pointed at both ends, forming the cen- 

 tral axis of the internal skeleton, and the basis of the 

 vertebral column. Directly above the spinal rod, on its 

 dorsal side, lies the spinal marrow (medulla spinalis), like- 

 wise originally a straight but internally hollow cord, pointed 

 at both ends. This forms the principal piece and centre of 

 the nervous system in all Vertebrate animals. (Compare above 



