Reactions of Isopods 445 



Table II is a summary of the vigor of responses made by 

 ten individuals each Asellus of Csecidotea. The tests were made 

 on various parts of the body by bristles numbered i, 2, 3,. No. 

 I was a pig bristleo.3 mm. in diameter, No. 2 a human hair, andNo. 

 3 a fine camel's hair. In the first column to the left are designated 

 the parts of the animals' body touched. In the successive triple 

 columns to the right of the first column are indicated how many of 

 the ten individuals experimented upon were extremely responsive 

 when the various parts were stimulated by bristles i, 2, 3, how 

 many were strongly responsive, fairly responsive, slightly respon- 

 sive and not responsive to stimulation upon the flagellum of the 

 antenna by bristle No. i, two were fairly responsive, six were 

 slightly responsive, and one was not responsive at all. To stimu- 

 lation upon the anntenules five Aseullus were j/ro/z^/jy responsive 

 to No. I, six to No. 2 and two to No. 3, etc. 



This summary mdicates clearly that Caecidotea is more sensitive 

 to mechanical stimulation than Asellus is. Of the individual tests 

 made upon the ten Caecidotea 88 responses from the 240 trials 

 indicated extreme sensitiveness and 108 indicated that the animal 

 was strongly sensitive. The same test upon Asellus produced 

 only 7 extreme responses indicating extreme sensitiveness and 82 

 strong responses. Of the whole number of tests with the three 

 bristles, only 2 tests aroused no response in Caecidotea, though 30 

 tests failed to produce reactions in Asellus. Bristle No. i produced 

 35 extreme responses with Caecidotea and only 5 with Asellus. 

 With bristle No. 3, 25 extreme responses were gotten from Caeci- 

 dotea and none from Asellus. 



The responsiveness of Caecidotea to the different bristles is 

 very much the same, there being 35, 28 and 25 extreme responses 

 to bristles Nos. i, 2, and 3 respectively. With Asellus there is a 

 very rapid falling off in responsiveness to the smaller bristles 

 indicating a decided decrease in sensitiveness. The different 

 bristles gave 5, 2 and to extreme responses and 52, 20 and 10 

 strong responses, respectively, indicating that with Asellus the 

 predominating grade, of responsiveness to the coarsest bristle 

 used is only of the grade, strongly sensitive, and that this respon- 

 siveness is much less pronounced with the finer bristles with which 



