THE AMPHIOXUS. 199 
of all the Vertebrate animals known tous. 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. Butstill 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 
