EBEN J. CAREY 359 



The influence of the organism as a whole in subjugating its de- 

 pendent parts is convincingly shown by Loeb (1916) in his regenera- 

 tion experiments on Bryophyllum calycinum and in his experiments 

 on Ambly stoma larva (1897). This influence is exerted through the 

 blood stream by means of "hormones." The sound mechanistic 

 attitude of Loeb toward development may be seen in the following 

 statement: "As soon as we can show that a life phenomenon obeys 

 a simple physical law there is no longer any need for assuming the 

 action of non-physical agencies" (1916). 



The object of this paper is not, however, to discuss historically the 

 views of these various authors, but to emphasize certain facts in the 

 development of muscle tissue hitherto overlooked. It is a well known 

 fact that the embryo presents differential rates of growth. It is 

 desired, therefore, to emphasize the fact that in embryological devel- 

 opment there are zones of unequal or differential growth, and that the 

 effects of these zones of growth are factors in histogenesis. The active 

 and less active zones are defined with reference to the rate of cell 

 division per mm. of cross-section. This principle was deduced from a 

 series of studies on osteogenesis and myogenesis begun in 1914. Pre- 

 vious reports of a part of this work have been presented to the As- 

 sociation of American Anatomists (Carey, 1917, 1918, 1919). 



It will be illuminating to search for the cellular forces outside of 

 the immediate differentiating zone under observation. This search 

 necessitates lower magnifications in order to enlarge our field of view. 

 Heretofore, cytological differentiation has been studied per se, with 

 magnifications of 1,000 to 2,000 diameters which considerably re- 

 duce our range of view. The higher magnifications are profitable in 

 revealing cytological detail but the interpretation of the process is 

 lost unless, in conjunction with the higher, intermediate magnifica- 

 tions are used. The employment of all magnifications of the micro- 

 scope in connection with naked eye studies will reveal the interaction 

 of related developing parts. 



Early Development of the Descending Colon of the Pig. 



The attention of the writer was directed to the fact, after plotting 

 hundreds of intestinal epithelial mitotic figures, that these figures were 

 usually confined to some definite region of the circumference of a single 



