142 METAMORPHOSES OF MAN 



This problem remained unexplained till about the 

 first third of the present century. 



It is quite true that Bernard de Jussieu had dis- 

 covered the hydra^s eggs ; that Cavolini, then residing 

 at the sea-side, had observed the eggs, or the whiffling 

 germs , as he termed them, of the polyps, and had seen 

 them attach themselves to some solid body and give 

 rise to a new polypidom -* and that many other facts 

 had been recorded. Nevertheless, the problem was 

 left in nearly as much obscurity as ever, until Messrs. 

 Audouin and Milne Edwards declared that the com- 

 pound ascidians deposited true ova, from which sprung 

 larvse, at first restlessly active, but which eventually 

 became fixed, and developed a new colony. f This 

 important discovery, which was at first denied, but 

 afterwards confirmed by several naturalists, was the 

 start-point of a series of most valuable researches made 

 by Milne Edwards ; and we shall now proceed to give 

 a brief resume of them. J 



The ascidians are marine mollusks without shells, 

 and may be divided into three distinct groups. In 

 some the individuals are free and isolated, and are 

 hence called simple ascidians ; in the second division 

 the members are loosely connected by trailing root- 

 like prolongations, and are termed social ascidians ; 

 whilst the individuals of the third section are fused as 



* " Memorie per servire alia Storia dei Polypi marini," 1789. 



t " Observations sur les Ascidies composees des cotes de la 

 Manche en 1834 et 1839." Since that date Van Beneden has 

 observed the same forms of reproduction among the simple ascidians. 

 — "Kecherches sur l'Embryogenie, 1'Anatomie, et la Physiologie 

 Ascidies simples," 1846. 



X' " Resume des Kecherches sur les Animaux sans vertebres, 

 faites aux iles Chausey," 1828. 



