252 A. M. Bania 



with one another. Their responses, however, are of a different 

 nature from those of Asellus. The Cascidotea do not collect in 

 bunches, but usually move away from one another very quickly 

 at the slightest mutual contact. The thigmotactic response, 

 then, is not, as with Asellus, positive, but on the contrary very 

 decidedly negative. 



Slight, non-essential modifications were made from time to 

 time in the apparatus described above in order the better to fit 

 it for particular conditions of experimentation. 



2. Asellus 

 A. Following Previous Exposure to Light 



In considering the reactions of the two species to special light 

 conditions after their previous exposure to diffuse daylight, Asellus 

 will be discussed first, although it is to be borne in mind that the 

 corresponding experiments with the two species were carried on 

 in quick succession. 



Asellus was found to be not very responsive to light, and dur- 

 ing the earlier experiments seemed so capricious that httle uni- 

 formity could be detected in its responses. However, with 

 improved conditions of experimentation and with better knowl- 

 edge of the actions of the species in general, the responses were 

 ultimately found to be fairly definite and uniform. 



To intensities below about 2.5 candle meters (CM.), however, 

 Asellus is not at all responsive. This conclusion is based on the 

 results of a number of experiments. Table i shows the results 

 of an experiment with an intensity approximately i CM., pro- 

 duced under the following conditions: 5 c.p. incandescent lamp 

 at 2.25 meters from the middle of the tank. 



In this table and in the following ones, showing results of experi- 

 ments with horizontal illumination, the same general plan m the 

 arrangement of data has been followed. In the first column, at 

 the left, are indicated the time at which the experiment started 

 and also the epochs at which the various observations were made. 

 The six succeeding columns at the right of this one show the num- 

 bers of individuals in each of the six sections of the tank at each 



