Chap. VI. 
AFFINITIES AND GENEALOGY. 
205 * 
negative characters ; it can hardly be said to possess a 
brain, vertebral column, or heart, &c. ; so that it was 
classed by the older naturalists amongst the worms-. 
Many years ago Prof. Goodsir perceived that the 
lancelet presented some affinities with the Ascidians, 
which are invertebrate, hermaphrodite, marine crea- 
tures permanently attached to a support. They hardly 
appear like animals, and consist of a simple, tough r 
leathery sack, with two small projecting orifices. They 
belong to the Molluscoida of Huxley — a lower division 
of the great kingdom of the Mollusca ; but they have 
recently been placed by some naturalists amongst the 
Yermes or worms. Their larvae somewhat resemble 
tadpoles in shape , 21 and have the power of swimming 
freely about. Some observations lately made by M„. 
Kowalevsky , 22 since confirmed by Prof. Kuppfer, will 
form a discovery of extraordinary interest, if still further 
extended, as I hear from M. Kowalevsky in Naples he 
has now effected. The discovery is that the lame of 
Ascidians are related to the Yertebrata, in their manner 
of development, in the relative position of the nervous 
system, and in possessing a structure closely like the 
chorda dorsalis of vertebrate animals. It thus appears, 
if we may rely on embryology, which has always proved 
the safest guide in classification, that we have at last 
gained a clue to the source whence the Yertebrata have 
21 I had the satisfaction of seeing, at the Falkland Islands, in April,, 
1833, and therefore some years before any other naturalist, the loco- 
motive larvae of a compound Ascidian, closely allied to, but apparently 
generically distinct from, Synoicum. The tail was about five times as 
long as the oblong head, and terminated in a very fine filament. It 
was plainly divided, as sketched by me under a simple microscope, by 
transverse opaque partitions, which I presume represent the great cells 
figured by Kowalevsky. At an early stage of development the tail was 
closely coiled round the head of the larva. 
22 ‘ Memoires de l’Acad. des Sciences de St. Petersbourg,’ tom. x. 
No. 15, 1866. 
