254 THE DOCTRINE OF DESCENT. 
let also, the anterior end of the primitive intestine 
becomes the branchial cavity. But with reference to the 
vertebrate animals, the most important parts of the Asci- 
dian larva are the following. It possesses a true spinal 
cord with a vesicularly expanded brain (va). The distri- 
bution and position of this organ agrees accurately with 
the corresponding parts of the vertebrate animal, and 
Kupfer has even discerned the rudiments of nerves 
(sss), which, if the observation is confirmed, will still 
more incontrovertibly establish the homology of the 
organ in question with the spinal cord of the Vertebrata 
and the nerves proceeding from it in pairs. But we 
know that it is not the spinal cord alone, but its combi- 
nation with the vertebral column which constitutes the 
characteristic feature of the vertebrate animal. This ver- 
tebral column the Ascidian larva likewise possesses (c) 
in the form of the noto-chord, and, as in the vertebratc 
animal, this embryonic vertebral column lies between 
the intestine and the spinal cord. So far goes the ac- 
cordance; henceforth, the development of this part, so 
important to the vertebrate animal, becomes retrogres- 
sive in the Ascidian. The rudder-like tail, with the 
spinal cord contained in it, and the noto-chord, are cast 
off when the animal becomes fixed; the larval brain 
which promised so well, shrinks into an insignificant 
nervous ganglion, and the complete animal gives no 
cause for suspecting its analogy with the Vertebrata. 
These laborious observations prove that the Vertebrata 
are not the sole proprietors of the spinal cord and verte- 
bral column, but received these organs as a heritage from 
lower grades of organization as their progenitors. it 
does not occur to the Darwinists to regard man as the 
