30 METAMORPHOSES OF MAN 



liest stage of a mass of homogeneous, transparent, gela- 

 tinous matter, which has little or no distinct structure. 

 M. Dujardin has judiciously named this elementary 

 substance sarcode, a term which signifies, as it were, 

 the road or highway upon which the tissues set out on 

 their journey to their adult condition. From this mass 

 of living matter all the anatomical elements are pro- 

 duced, and then, by the union of these latter, the 

 various organs of the body are formed also. All 

 physiologists who have devoted their attention to the 

 development of mammalia, and of the lower inver- 

 tebrata, agree upon this point ; and even when they do 

 not draw the conclusion in set terms, it follows from 

 their researches. 



But then, is the sarcode directly transformed into 

 tissue, or is there a series of intermediate changes ? 

 In answering this question, we come to a doctrine 

 which has been almost universally believed in, in 

 Germany, for the last twenty years, and which many 

 distinguished naturalists of other countries have put 

 their trust in also. We allude to that hypothesis 

 which Schwann, a pupil of the famous Miiller, bor- 

 rowed in part from botanical science, and applied to 

 zoology, under the title of the Cell theory. 



Botanists admit the existence in plants of a primary 

 anatomical element, which may be converted by a 

 series of modifications into the several vegetable 

 tissues and organs. * This element they term a 

 cell; it is a small vesicle formed of a single or double 



* For some years the theory to which I allude was regarded as 

 having no exceptions ; but the progress of knowledge shows us 

 that it only applies within certain limits even to the branch of 

 natural science which at one time appeared to bear it out fully. 



