290 COLLEGE ZOOLOGY 



always like that of the one removed. For example, Figure 208 

 shows an antenna which regenerated in place of an eye in a 

 marine crustacean, Palcemon. 



Autotomy. — Perhaps the most interesting morphological 

 structure connected with the regenerative process in Cambarus 

 is the definite breaking point near the bases of the walking legs. 

 If the chela? are injured, they are broken off by the crayfish at 

 the breaking point. The other walking legs, if injured, may be 

 thrown off at the free joint between the second and third segments. 

 A new leg, as large as the one lost, develops from the end of the 

 stump remaining. This breaking off of the legs at a definite 

 point is known as autotomy, a phenomenon that also occurs in 

 a number of other animals. The leg is separated along the break- 

 ing point by several successive muscular contractions. It has 

 been shown " that autotomy is not due to a weakness at the 

 breaking point, but to a reflex action, and that it may be brought 

 about by a stimulation of the thoracic ganglion as well as by a 

 stimulation of the nerve of the leg itself." (Reed.) 



The power of autotomy is of advantage to the crayfish, since 

 the wound closes more quickly if the leg is lost at the breaking 

 point. No one has yet offered an adequate theory to account 

 for autotomy. It is probably " a process that the animal has 

 acquired in connection with the condition under which it lives, 

 or, in other words, an adaptive response of the organism to its 

 condition of life." (Morgan.) 



Behavior. — When at rest, the crayfish usually faces the en- 

 trance to its place of concealment, and extends its antennae. It 

 is thus in a position to learn the nature of an approaching object 1 

 without being detected. Activity at this time is reduced to 

 the movements of a few of the appendages and the gills; the 

 scaphognathites of the second maxilla? move back and forth, 

 baling water out of the forward end of the gill chambers; the 

 swimmerets are in constant motion creating a current of water; 

 the maxillipeds are likewise kept moving; and the antennas and 

 eye-stalks bend from place to place. 



