248 M. Van Beneden on the Physiology of the Simple Ascidians. 
XXXIII.— Abstract of a memoir on the Embryogeny, the Anatomy 
and Physiology of the Simple Ascidians, &c. By M. Van 
BENEDEN, Professor in the Catholic University of Louvain, &.* 
I nave the honour to present to the Academy a new memoir on 
some animals that inhabit our coasts. It is a sequel to those I 
have already communicated, and is entitled ‘ Recherches sur 
VPembryogénie, l’anatomie et la physiologie des Ascidies simples,’ 
&c. Ina short time I hope to lay before you a work on the em- 
bryogeny of the Acephala, and another on the Acarides, on which 
I have been occupied for several years. 
To the present time I ‘have observed four species of simple 
Ascidie on our coasts, three of which appear to be undescribed. 
The abundance of one of them on the oyster-beds at Ostend, and 
to which, because of its form, I have given the name ampulloides, 
has permitted me to study with care both its anatomy and its 
growth ; and I have seen all the phenomena of its embryo-evo- 
lution from the first appearance of the egg and of the spermatozoa 
in the sexual organs. When young the Ascidia is nomade, as 
Milne Edwards stated in 1828; when adult it is fixed, and in 
this last stage of its existence, all the functions are reduced to 
those of nutrition and of reproduction. vets 
What relates to the embryogeny has, in an especial manner, 
engaged my attention. It 1s, we may say, a new science, and 
yet it almost already claims its due place, for without its guidance 
we cannot take a step towards the solution of the highest ques- 
tions in anatomy, physiology and zoological classification. Hence 
the reason which has induced me to give it here the same pre- 
ference it has in my previous memoirs. © 
Cuvier and Savigny have carefully anatomized these Aseidie ; 
and Sars in Norway, Dalyell in Scotland, and Milne Edwards in 
France have studied their genesis with equal care. The favour- 
able circumstances in which I am placed have enabled me to add 
to the excellent works of these naturalists some new facts and 
rectifications of others. It seemed to me also that it would be 
not uninteresting to represent, in a continuous series, all the me- 
tamorphoses which the Ascidie undergo in their different ages. 
The memoir is divided into four parts. The first is historical ; 
the second contains the exposition of their anatomy; the third 
has the embryogeny for its subject ; and the fourth comprises 
some reflections on the place which the Ascidians ought to have 
in the animal scale, and an enumeration of the species I have 
observed on our shores up to this date. 
Hitherto no one has seen in the Ascidie either eyes or any 
* Extrait du tome xiii. no. 2. des Bulletins de l’Académie Royale de 
Belgique. 
