AFFINITIES AND GENEALOGY. 155 



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 

 creatures permanently attached to a support. They hardly ap- 

 pear like animals, and consist of a simple, tough, leathery sack, 

 with two small projecting orifices. They belong to the MoUus- 

 coida of Huxley— a lower division of the great kingdom of the 

 Mollusca; but they have recently been placed by some natural- 

 ists amongst the Vermes or worms. Their larvae somewhat 

 resemble tadpoles in shape,'" and have the power of swimming 

 freely about. M. Kovalevsky" has lately o))served 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 dorsalis of 

 vertebrate animals; and in this he has been since confirmed by 

 Prof. KupfCer. M. Kovalevsky writes to me from Naples, that 

 he has now carried these observations yet further; and should 

 his results be well established, the whole will form a discovery 

 of the very greatest value. Thus, if we may rely on embryology, 

 ever the safest guide in classification, it seems that we have at 

 last gained a clue to the source whence the Vertebrata were de- 

 rived."^ We should then be justified in believing that at an ex- 

 tremely remote period a group of animals existed, resembling in 

 many respects the larvae of our present Ascidians, which diverged 

 into two great branches — the one retrograding in development 

 and producing the present class of Ascidians, the other rising to 

 the crown and summit of the animal kingdom by giving birth 

 to the Vertebrata. 



^ At the Falkland Islands I had the satisfaction of seeing, in April, 

 1S33, and therefore some years before any other naturalist, the loco- 

 motive larvae of a compound Ascldian, closely allied to Synoicum, 

 but apparently generically distinct from it. The tail was about five 

 times as long as the oblong head, and terminated in a, very fine fila- 

 ment. It was, as sketched by me under a simple microscope plainly 

 divided by transverse opaque partitions, which I presume represent 

 the great cells figured by Kovalevsky. At an early stage of develop- 

 ment the tail was closely coiled round the head of the larva. 



24 'Memoires de I'Acad. des Sciences de St. Petersbourg,' tom. x. 

 No. 15, 1S66. 



25 But I am bound to add that some competent judges dispute this 

 conclusion; for instance, M. Giard, in a series of papers in the 'Arch- 

 ives de Zoologie Experimentale,' for 1872. Nevertheless, this natural- 

 ist remarks, p. 281, "L'organisation de la larve ascidienne en dehors 



de toute hypothese et de toute theorie, nous montre comment la 

 nature pent produire la disposition fondamentale du type vertebre 

 (I'existence d'une corde dorsale) chez un invertebre par la seule con- 

 dition vitale de I'adaptation, et cette simple possibilite du passage 

 'supprime I'abime entre les deux sous-regnes, encore bien qu'en ignore 

 'par ou le passage s'est fait en realite." 



