440 A. M. Bant a 



The work was done at the Museum of Comparative Zoology at 

 Harvard College under the direction of Prof. G. H. Parker, to 

 whom grateful acknowledgement is made. 



I. EXPERIMENTS WITH MECHANICAL STIMULATION 

 /. JVith Bristles 



The first method of testing the sensitiveness of the two animals 

 to mechanical stimulation was by touching various parts of their 

 bodies with delicate bristles. Six bristles ranging from 0.3 mm. 

 in diameter to the finest camel's hair were employed at first, but 

 it was found unnecessary to use so many and finally three were 

 selected for use, a coarse pig bristle 0.3 mm. in diameter, a human 

 hair and a fine camel's hair. The bending strain of the three 

 bristles was 1.7 grams, .0025 gram, and .001 gram respectively. 

 These will be referred to in future as bristles i, 2, and 3. They 

 were firmly fixed to the ends of slender glass rods by, means of 

 small rubber bands. About one centimeter of the bristle extended 

 beyond the end of the rod. 



The animals to be experimented with were placed each in a 

 separate glass dish containing water to a depth of about two centi- 

 meters. Dishes with either ground-glass or wax-covered bottoms 

 were used, since a smooth glass surface afforded no foothold for 

 the anmials and they were unable to move with certainty upon it. 

 Since Cnecidotea normally lives in water a at temperature near 

 ii°C., the water was kept at about this temperature during the 

 experiments. Asellus, being normally subjected to a considerable 

 range of temperatures, would probably not be much influenced 

 by slight changes of heat and cold, but for the sake of uniformity 

 it was kept and experimented upon at the same temperature as 

 Caecidotea. 



One specimen of each species was tested at a fme. The dishes 

 containing the two individuals to be used were placed in a larger 

 dish of water so that the temperature of the two animals would 

 remain the same. A thermometer was kept between the two small 

 dishes. From time to time cold water or bits of ice were added to 



