792 W. T. CALMAN. 



Instead of being limited to comparatively trivial characters 

 and giving rise to varieties or " petites especos " as in de 

 Vries's examples, the mutations of the Atyidcio affect characters 

 of generic importance. Bouvier believes that the course of 

 evolution from the more primitive Caridina to the specialised 

 Atya has been discontinuous, proceeding at a single step 

 from Caridina to Ortmannia and again from Ortmannia 

 to Atya, and that the species mentioned remain in the con- 

 dition of instability accompanying the transition from one to 

 the other. It is also implied, although Bouvier does not dwell 

 on the point, that these genera are polyphyletic and have 

 originated independently in several regions of the globe. 



There is still another possibility, not alluded to by Bouviei", 

 that deserves mention here, namely, that the apparent di- 

 morphism is due to heteromorphic regeneration of the chelipeds 

 after mutilation. Many cases are now known among Arthro- 

 poda in which regenerated appendages depart from the norniiil 

 type, and not infrequently revert to a simpler and more 

 primitive form ("regeneration hy j)oty pique " of Giard). 

 Although the chelipeds of many Atyida) readily break off 

 from the body in preserved specimens, it seems very impro- 

 bable that this mutilation should happen so frequently in 

 nature that 50 per cent, of the specimens collected would 

 have regenerated limbs ; nor is it less improbable that all four 

 chelipeds would be removed simultaneously^; and the experi- 

 ments of Bordage, described below, lend no support to this 

 suggestion. 



Professor Bouvier pointed out the desirability of testing 

 his conclusions by observation and experiment on the living 

 animals, and it was at his suggestion that Bordage undertook 

 the researches of which the results are presented in his recent 

 papers ('08, '09a, '09b). On the island of Reunion Ort- 

 mannia alluaudi, with its mutation Atya serrata, occurs 

 abundantly in mountain streams at altitudes above 300 

 metres. Owing to the high temperature prevailing at the 



' Only one case bus been noticed in wbicli one of tbe chelipeds 

 differed from tbe others (see above, p. 790, footnote). 



