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, 

 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 

 Vermes 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 larvae of 

 Ascidians are related to the Vertebrata, in their manner 

 of development, in the relative position of the nervous 

 system, and in possessing a structure closely like the 

 chorda dor salts 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 Vertebrata 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,' torn. x. 

 No. 15, 18G6. 



