Literary Notices. 287 



from him regarding the earher differentiation of neurohlasts and regard- 

 ing the migration of cells into the ventral root from the neural tube. 

 There would seem to be important differences between the histogenesis 

 of the ventral nerves in the shark and the chick when we compare this 

 account with Bethe's. o. s. s. 



Jennings, H. S. Asymmetry in Certain Lower Organisms, and its Biological 

 Significance. Art. XVI, pp. 315-337. 



In addition to the commonly recognized radially symmetrical and 

 bilaterally symmetrical types of organism, there is, as Jennings points 

 out, another type of structure which may be called the spiral type, since 

 the organisms necessarily move in a spiral course, or the one-sided un- 

 symmetrical type. An unsymmetrical organism, were it not for rota- 

 tion about its long axis, would move in a circular instead of a spiral 

 course. 



Organism.^ which move in a spiral course maintain a definite posi- 

 tion with reference to the axis of the spiral ; the same surface always 

 faces outward, the same inward. In most of the unsymmetrical or- 

 ganisms it is noticable that reactions do not differ in form according to 

 the location of the stimulus, as in more highly organized animals, but 

 that no matter which side is stimulated the animal always turns in t,he 

 same direction. 



The relation of structure to behavior is considered iu detail in 

 case of the Infusoria and Rotifera, and the author concludes that there 

 is always striking adaptation of structure to the "mode of life and 

 movement." 



In criticism of the author's conclusions one might say, certainly 

 there can be no doubt of the close correlation of structure with mode 

 of life, but is it so clear that structure is an adaptation to behavior 

 rather than behavior to structure? Rather, it would seem impossible 

 that either could in all cases be an adaptation to the other. Possibly 

 our safest position would be to consider both adaptations to something 

 which is not to be described as either structure or mode of life. 



The paper emphasizes the importance of studying structure and 

 behavior side by sile, and of attempting to arrive at definite knowd- 

 edge of their correlation. r. m. y. 



Floyd, R. A Contribution to the Nervous Cytology of Periplaneta orientalis, 

 the common Cockroach. Art. XVII, pp. 341-357, pis. 25-27. 



By a careful series of experiments the author has determined the 

 effect of various fixing reagents on the structure of nerve cells from 

 the thoracic ganglia of the cockroach. Tissues fixed in vo.m Rath's 



