THE BAY OF BISCAY. 245 



and throws itself into the liquid under the form of a 

 small and irregularly spherical larva, bristling all 

 over with vibratile cilia. 



Such are briefly the phenomena presented by the 

 fertilised egg of the Hermella. In twelve or at most 

 fifteen hours, this egg becomes transformed into an 

 animal, which swims about, stops and guides itself, 

 and thus gives evident signs of spontaneity. The 

 same egg, if left in the liquid without being brought 

 in contact with the fertilising element, becomes de- 

 composed in about forty or fifty hours. We must 

 not, however, suppose that it is the less active on 

 this account. The characteristic activity of the first 

 phases of development are manifested here no less 

 than in the fertilised egg. The yolk dilates and 

 contracts, the spot and vesicle disappear, the vitellus 

 undergoes cleavage, and becomes thinner. For the 

 first few hours it is almost impossible to distinguish 

 a fertilised from a non-fertilised egg. In the latter, 

 however, the movements increase in rapidity while 

 they diminish in regularity, and instead of result- 

 ing in the organisation of a new being, they terminate 

 in the destruction of the germ. If, however, we take 

 some of these eggs which seem very nearly decom- 

 posed and bring them in contact with the fertilising 

 corpuscles, their movements will slacken and become 

 more regular, and we may even frequently obtain 

 numerous swarms of larvae from eggs that have been 

 deposited for nearly forty hours. 



These facts, which I have repeatedly verified, 

 appear to me to be thoroughly conclusive. They 

 teach us that the movements, which have their seat 



it 3 



