318 'Journal of Comparative Neurology and Psychology. 



the method. In this polemic, as in later work, is seen the positive, 

 definite character of the anthor's thonght, with no appreciation for 

 shadings, transitions or compromises; sharpness of concept and of 

 distinctions, black or white, is demanded everywhere. 



The Work ojs^ the Sea Ukcjlin. 



It is in the series of papers on the sea urchin (10, 1:^, Vo, 10, 19, 

 •20) that the author "strikes his pace" and l)rings out clearly the 

 important phenomena which form the basis for his peculiar system 

 of concepts. The plan of investigation is to work out the structure of 

 Ihe muscular, nervous and skeletal systems and the way they act 

 together to produce the characteristic behavior of the animal ; to work 

 out "the biological plan" of the sea urchin. The paper on Reflexes 

 in the Sea Urchin (12) gives a general sketch of this biological plan 

 and the main reflexes which make up the behavior ; the structure of 

 the simi)le nervous system, the reflexes of the pedicellarite, the spines, 

 the tube-feet, the teeth, are briefly described. Then followed in 

 1899 a thorough detailed paper on the physiology of the pedicellarise 

 (10), a paper which must form the point of departure for all further 

 work on these organs. The history of our knowledge of the pedi- 

 cellari*, their structure, the ditt'erent sorts, their uses and particu- 

 larly the laws of their movements, are developed in great detail. 

 In 1900 came a similarly thorough, and perhaps still more impor- 

 tant, study of the movements of the spines (19). Special studies 

 were made of the reactions of the spines to light and shadow (1-3, 

 20) ; for the purpose of obtaining species favorable for this work 

 the author made a tri]) to the cast coast of Africa; the outtit for this 

 trip is described in a separate paper (21). 



In general, v. Uexkiill found that the various organs of the sea 

 urchin, — each spine, each pedicellaria, — can perform a niiiii1)er of 

 different acts or reflexes, and that these reflexes occur to a large 

 degree independently of each other, so that they may occnr when the 

 organ in question is isolated on a small piece of the shell. Thus each 

 organ is a "reflex ])erson.'' Yet all the difl'eriiig reflexes of these 

 various "■pci-soiis" are of such a character that they woi'k together 

 in a sysli'iuatic way to perfoi-m the necessary fiiuctioiis of the animal. 



