RELATION OF ASCIDIANS TO VERTEBRATES. 397 
point of difference from othey animals in the development 
of all vertebrates is seen in the formation of the dorsal 
ridges, and their closing to form a nerve-canal. This mode 
of formation of the nervous system is characteristic of the 
vertebrates alone, except the Ascidians. Another primary 
character allying the Ascidians to the vertebrates, is the 
presence of a chorda dorsalis, first seen in the adult Appen- 
dicularia by J. Miller. This organ is regarded by Kowal- 
evsky to be functionally, as wellas genetically, identical with 
that of Amphioxus. This was a startling conclusion, and 
stimulated Professor Kupffer, of Kiel, to study the embry- 
ology of the Ascidians anew. He did so, and the results this 
careful observer obtained led him to fully endorse the con- 
clusions reached by Kowalevsky, particularly those regarding 
the unexpected relations of the Ascidians to the vertebrates, 
and it would appear from the facts set forth by these emi- 
nent observers, as well as Metschnikoff, Ganin, Ussow, and 
others, that the vertebrates have probably descended from 
some type of worm resembling larval Ascidians more perhaps 
than any other vermian type, though it is to be remembered 
that certain tailed larval Distome appear to possess an organ 
resembling a chorda dorsalis, and farther investigation on 
other types of worms may lead to discoveries throwing more 
light on this intricate subject of the ancestry of the verte- 
brates. At any rate, it is among the lower worms, if any- 
where, that we are to look for the ancestors of the Vertebrates, 
as the Coelenterates, Echinoderms, the Mollusks, Crustacea 
and Insects, are too circumscribed and specialized groups to 
afford any but characters of analogy rather than affinity. 
For example, the cuttlefish, with its ‘‘ bone,” brain-cap- 
sule and highly-developed eye, is, on the whole, more remote 
from the lowest vertebrate, Amphioxus, than the Appendi- 
cularia or the larval Ascidian. 
Certain (three) species of Molgula have been found by 
Lacaze-Duthiers to have a nearly direct development, not 
producing tailed young. There is a slight metamorphosis, 
however, the young having five temporary, long, slender 
processes. In Ascidia ampulloides the larva has a tail, no- 
tochord and pigment spots. which are wanting in the young 
