THE CRAYFISH AND ARTHROPODS IN GENERAL 219 





The life of a single individual extends over a period of about three 

 or more years. Table IX presents the main facts of larval de- 

 velopment during the first summer (159). Table X gives the 

 age and size of a single specimen during its entire life. 



Regeneration. The crayfish and many other Crustaceans 

 have the power of regenerating lost parts, but to a much more 

 limited extent than such animals as Hydra and the earthworm. 

 Experiments have been performed upon almost every one of the 

 appendages as well as the eye. The second and third maxillipeds, 

 the walking legs, the swimmerets, and the eye have all been 

 injured or extirpated at various times and subsequently renewed 

 the lost parts. Many species of crayfish of various ages have been 

 used for these experiments. The growth of regenerated tissue 

 is more frequent and rapid in young specimens than in adults 

 (184). 



The new structure is not always like that of the one removed. 

 For example, when the annulus containing the sperm receptacle 

 of an adult is extirpated, another is regenerated, but, although this 

 is as large as that of the adult, it is comparable in complexity to 

 that of an early larval 

 stage (161). A more 

 remarkable phenome- 

 non is the regeneration 

 of an apparently func- 

 tional (tactile) an- 

 tenna-like organ in 

 place of a degenerate 

 eye which was removed 

 from the blind crayfish, 

 Cambarus pellucidus 

 testii. In this case a 

 non-functional organ FIG. 117. Diagram showing antenna-like organ 

 was replaced by a func- regenerated in place of an eye of Palae- 



tional one of a differ- mon ' (From Morgan after HerbsL) 

 ent character (190). The regeneration of a new part which differs 



r 



