46 RAMBLES OF A NATURALIST. 



frog. The elements of the yolk or Vitellus group 

 themselves in different manners, and finally present 

 four distinct masses thrust into the centre of the 

 e gg by a whitish and granular substance. The 

 process of development goes on rapidly, and we 

 soon have before us a sort of spherical sac, whose 

 interior is entirely occupied by the remainder of the 

 Vitellus. No organ is as yet visible; we merely 

 observe two small coloured spots, which indicate 

 the place of the eyes. In this state of extreme im- 

 perfection, the young Terebella bursts through the 

 membrane of the egg; at this period the body is 

 rounded, and bristling in all parts with vibratile 

 cilia. In this condition it resembles certain of the 

 Infusoria, or perhaps still more those reproductive 



best able to play their part in it, M. Dumas was appointed chemical 

 demonstrator at the Ecole Polytechnique, and the final direction of 

 his studies was thus determined. We need scarcely here refer to the 

 eminent part which he has played as a chemist, both independently, 

 by his own researches, and through the numerous pupils who have 

 accepted him as their leader, nor will it be necessary here to show 

 how the ideas which he advocated have progressively replaced the 

 electro-chemical theory of the illustrious Berzelius. But we ought 

 to observe, that in the midst of his various successes and engage- 

 ments, M. Dumas has never entirely forgotten the science which 

 constituted the object of his early studies. For the last twelve or 

 fifteen years his labours have been directed towards physiology, and 

 especially to the application of chemistry to that science. By 

 the influence which he has exerted in this direction, he must be 

 considered as the actual leader of physiological chemistry, appearing 

 in this respect, as the successor of Van Helmont, Sylvius, and 

 Fourcroy. The present is not the place in which to discuss these 

 doctrines, but I shall undoubtedly some day have occasion to revert 

 to the subject, when I shall consider the labours and views of M. 

 Dumas in relation to organised beings. 



