258 J. S. NICHOLAS 



extirpation of the sense organs in the larvae. Unfortunately, 

 all of the animals so treated failed to survive. The present work 

 was started in ^he fall of 1919 in order to get control results for 

 the data which it is hoped can later be obtained upon adult forms 

 which have been operated upon in early stages of development. 



1 take pleasure in thanking Dr. Henry Laurens, under whose 

 direction the work has been carried on, for many helpful sugges- 

 tions and much useful criticism. The general observations upon 

 the behavior of the operated larvae here described were made by 

 Doctor Laurens, who performed the necessary operations in the 

 spring of 1917.- 



MATERIAL AND METHODS 



The same general method of approach was used as in Burr's 

 ('16) work, i.e., removing the embryonic anlage of the sense 

 organs. Since the method of operation has been described in 

 earlier papers (Laurens, '14, and Burr, '16), no description will 

 be necessary here. The operated larvae were kept in battery 

 jars stocked with the small Crustacea, Daphnia and Cypris, and 

 were allowed to grow to a length of about 25 mm. before any of 

 the observations were made. 



The adult animals, which were used for the main portion of 

 the work, were three individuals selected from a number that 

 had been sent to Doctor Laurens from Albuquerque, New 

 Mexico, in the spring of 1919. The same individuals were used 

 under all the different conditions described in the experimental 

 section, in order that the general control of the reactions might 

 be more accurate and a more reliable average of reaction obtained. 



The methods applied to these forms were mainly those which 

 have been used by Parker in his work on Fundulus and Ameiurus, 

 with an application of some of Risser's methods of experimenta- 

 tion. In all the experiments the test aquarium was cleansed 

 after each operation and filled with fresh water before continuing 

 the tests. 



2 The larvae on which the general observations were made were reared from 

 eggs sent to Doctor Laurens by Prof. C. P. Sigerfoos, in the spring of 1917. Dr. 

 W. C. Allee also was kind enough to send the author the eggs of A. tigrinum, 

 but unfortunately, owing to the vicissitudes of the journey and the shock of sub- 

 sequent operation, these animals did not survive. 



