802 MORPHOGENESIS 



the outer gelled layer of protoplasm of the intermediate zone creates a 

 circular zone of weakened elasticity or lowered resistance to the internal 

 pressure of the plasmasol" (p. 113). The differentiated anterior region 

 is therefore a prerequisite for normal streaming. 



Fragments of Paramecium caudatum were examined by Hosoi (1937) 

 in an effort to identify some of the forces involved in cyclosis. The 

 organisms were narcotized with iso-propyl alcohol (Bills, 1922) and 

 transversely sectioned at intervals along the primary axis. The type of 

 protoplasmic streaming concerned with the formation and release of 

 food vacuoles, the Schlundfadenstromung (Bozler, 1924), was evident 

 only in pieces possessing a large portion of the gullet, whereas cyclosis 

 in the strict sense occurred in all of the fragments within a few moments 

 after operation. Hosoi found that the Schlundfadenstromung and the 

 cyclical currents were largely independent phenomena, and that the 

 nuclei play no direct part in effecting either of these movements. His 

 suggestion that some special substances are attracted on the ecto-endo- 

 plasmic interface, which serve as the generating force of the streaming 

 movements, awaits further amplification. 



Physiological Gradients 



Outstandingly important in morphogenetic studies was Child's dis- 

 covery of physiological gradients in various animal types. After consider- 

 able experience with metazoan forms. Child (1914) directed his atten- 

 tion to Protozoa {Paramecium, Stentor, Stylonychia, Vorticella, and 

 Carchesium') , in which polarity is well defined. In these first experi- 

 ments the direct susceptibility or resistance method was used, with several 

 dilutions of KCN as the reagent in most cases. All of the forms showed 

 the greatest susceptibility in the apical region, although local regions of 

 still higher metabolic rate, such as the vacuolar regions in Paramecium, 

 were sometimes found. These experiments brought out the fact that a 

 close parallelism exists between the magnitude of the gradient and the 

 general morphological and physiological differentiation of the cell. 

 Peebles (1912) had previously noticed that anterior cuts cause greater 

 physiological disturbances than posterior cuts in Para?necium. 



The KCN susceptibility experiments were extended to amoeboid 

 forms by Hyman (1917). Unlike the clearly polarized types, Amoeba 

 was shown to have no permanent axial organization. A susceptibility 



