SIXTH LECTURE. 



THE INADEQUACY OE THE CEEL-THEORV OE 



DEVELOPMENT.^ 



C. O. WHITMAN. 



The doctrine of Schleiden and Schwann that hi cell -formation 

 lies the whole secret of organic development, has held the place 

 of a central axiom in biological work and speculation for over 

 half a century. All this time the cell has been, as it were, the 

 alpha and omega of both morphological and physiological 

 research. Regarded as a primary element of structure, it has 

 come to signify in the organic world what the atom and mole- 

 cule signify in the physical world. 



The traditional cell-standpoint has been most exactly defined 

 by Schleiden and Schwann. In his celebrated " Beitrage zur 

 Phytogenesis " (Miiller's Archiv, 1838), Schleiden sets forth 

 the cell-doctrine, which he limited to plants, in the following 

 words : ''Each cell leads a double life ; an independent one, 

 pertaining to its oiun developnient alone ; and another inci- 

 dental, in so far as it has become an integral part of a plants 



Schwann, in his classical Researches of 1839, extends the 

 same view to the entire organic world. 



''Each cell,'' he affirms, "is, zuithin certain limits, an individ- 

 ual, an independent zuhole. The vital phenomena of one are 

 repeated, entirely or in part, in all the rest. These ijidividuals, 

 however, are not ranged side by side as a mere aggregate, but 

 so operate together, in a manner unknoxvn to us, as to produce 

 an Jiarmoniojis zvhole.'' (Introduction, p. 2.) 



" The zuhole organism subsists only by means of the recipro- 

 cal action of the single elementary parts." 



The method of reasoning is precisely the same as we have 

 seen in some of the latest experimental studies on cleavage. 

 Witness the following : " If we find that some of these 



1 Read Aug. 31, at the Zoological Congress of tiie World's Columbian E.xpositiou. 



