C-RUST.UKANS IN CILET<>I>TKK( s ITHKS. 



103 



SHOWING THE NUMBER OF ANIMALS FOUND IN Chaloplerus TUBES. 



it has been increasing in numbers since then. The size of the 

 crustaceans collected at Woods Hole was about the same as 

 those measured by Enders ('05) at Beaufort. The maximum 

 width of the carapace recorded for Polyonyx was: female, 12.5 

 mm.; male, 9 mm.; Pinnixa: female, 12.5 mm.; male, 13 mm. 

 The proportion of tubes containing commensals was about the 

 same at the two places. 



Pinnotheres was not studied on account of its infrequent 

 occurrence, but the behavior of Pinnixa and Polyonyx was 

 observed in some detail. Both the latter crustaceans are thig- 

 motropic. When placed in a dish they usually stayed close in 

 the angles at the edge, or crawled under any objects that were 

 present. Pinnixa; often clung to each other or piled up in 

 groups. If supplied with glass tubes of suitable size, they 

 crawled into them and there remained indefinitely. 



In order to test the behavior of the commensals toward 

 Ch&topterus tubes an artificial tube was made in which their 

 movements could be observed. A glass tube was bent in the 

 form of a U and the tip of a Chcetopterus tube slipped over each 

 end where it was tied securely. This composi te tubewas placed 

 upright in a rectangular glass jar filled with sand so that the 

 glass tube could be observed through one side of the jar, though 

 only the leathery tube tips projected into the sea water above the 

 sand. The crustaceans were placed on the surface of the sand 

 and their behavior observed. Pinnixce usually walked to one 

 side of the jar where they burrowed into the sand and- remained 

 for several minutes; the Polyonyces moved quickly to the side 



