HUXLEY. 37 



cellulose wall of the plant, both representing the periplastic 

 element ; while the nuclei of the former represents the primor- 

 dial utricle, contents, and nucleus of the latter. With this all 

 who have considered the foregoing evidence will no doubt 

 agree ; but then he adds : " In the plant the primordial utricles 

 divide, separate, and the cellulose substance grows in between 

 the two. In young cartilage the same thing occurs : the cor- 

 puscles divide, separate, and the chondrin substance eventually 

 forms a wall of separation between the two. There is neither 

 endogenous development nor new formation in either case. 

 The endoplasts grow and divide, the periplast grows so as to 

 surround the endoplasts completely, and, except so far as its 

 tendency is to fill up the space left by their separation, there is 

 no evidence that its growth is in any way affected by them, 

 still less that it is, as is often assumed, deposited by them . . . 

 Finally, for the notion of the anatomical independence of the 

 cells, we must substitute that of the unity and continuity of 

 the periplastic substance in each case." 



Professor Huxley directs his attention primarily to the de- 

 velopment side of the question, putting in the foreground the 

 gradually increasing differentiation of the amorphous germ, 

 owing to its distinctively vital properties. So far, again, all will 

 now agree, but he goes on to say that the differentiation into 

 endoplast and periplast (i.e., a nucleated cell) is the first step, 

 and by the growth and differentiation of both these, tissues are 

 formed. " There is no evidence whatever that the molecular 

 forces of living matter (vis essentialis of Wolff, or the 

 vital forces of the moderns) are by this act of differentiation 

 localized in the endoplast to the exclusion of the periplast, or 

 vice versd. ... So far from being the centre of activity of the 

 actions, it would appear much rather to be the less important 

 histological element. The periplast, on the other hand, which 

 has hitherto passed under the name of cell wall, contents (?), 

 and intercellular substance, is the subject of all the most im- 

 portant metamorphic processes, whether morphological or 

 chemical, in the animal and in the plant. By its differentiation 

 every variety of tissue is produced ; and this differentiation is 

 the result, not of any metabolic action of the endoplast, which 



