THE LIVING ANIMAL 7 



which show selective habits, a considerable area must be cov- 

 ered. At the Tortugas laboratory I timed the movement of a 

 number of individuals of different families. The most rapid 

 movement was that of hidia diaphana which moved at its fast- 

 est speed at the rate of almost a millimeter per minute with an 

 average of about a centimeter per hour. A species of Discorbis 

 had an average speed of six millimeters per hour but it is a much 

 smaller form. Archaias aduncus moved for a short distance 

 at the rate of about five millimeters per hour. This species has a 

 relatively heavy thick test. Sorites duplex in a single observa- 

 tion moved for a time at the rate of about twelve millimeters per 

 hour. From observations made, it would seem that the test is 

 pulled along by the pseudopodia. 



When a feeding or moving specimen is disturbed, the pseudo- 

 podia are drawn back to the test but soon are sent out again. At 

 the Tortugas it was found that in all cases, if no actual injury 

 to the animal was made, the pseudopodia were thrust out again 

 within a period of five minutes from the time of contraction. 



Individuals, particularly of different species or genera, have a 

 decided repellant relation when their pseudopodia meet. It was 

 noted in several instances that such specimens when their 

 pseudopodia came in contact, changed their direction to avoid 

 one another. On the other hand when portions of the same in- 

 dividual had been cut in two, pseudopodia were rapidly thrown 

 out from each portion and in contact these fused and the two 

 parts moved toward one another and finally coalesced. 



At the Tortugas it was discovered that in specimens of Iridia 

 the tests were often left entirely by the animal which moved about 

 as a naked mass of protoplasm, with a free and comparatively 

 rapid movement. That the animal may withdraw from the test 

 and pass some time without one is very significant from the 

 standpoint of the method of growth. Growth of the test in those 

 species which have a single chamber has often been a subject 

 of speculation. If the test can be abandoned at will and another 

 secreted or made by collecting more material in the case of those 

 which have agglutinated tests, this difficulty is solved, and we 

 may also understand how various sedentary species are able to 

 collect various materials which are not common and make them 

 into tests. Given free movement and a power of discrimination, 

 which certain species seem to possess, it is not difficult to ex- 



