248 M. Van Beneden on the Phjsiology of the Simple Ascidians, 



XXXIII. — Abstract of a memoir on the EmhryogenT/, the Anatomy 

 and Physiology of the Simple Ascidians, ^c. By M. Van 

 Beneden, Professor in the Catholic University of Louvain, &c.* 



I HAVE 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 

 Fembryogenie, Fanatomie et la physiologic des Ascidies simples/ 

 &c. In a 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 

 AscidicB 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 phsenomena of its embryo-evo- 

 lution from the first appearance of the q^^ 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. 



What relates to the embryogeny has, in an especial manner, 

 engaged my attention. It is, 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 Ascidia ; 

 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 Ascidice undergo in their difi^erent 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 Ascidia either eyes or any 



* Extrait du tome xiii. no. 2. des Bulletins de TAcad^mie Royale de 

 Belgique. 



