NO. 1655). AMERICAX t<PECIES OF SYNALPHEU8—C0UTIERE. IQ 



very much the idea of species primitively widely dispersed ; perhaps 

 it will even render less uncertain the position of the continuous line 

 of coast along which the dispersion might have been made. It seems 

 to me that one might sketch this original distribution under the form 

 of a few waves of very great amplitude, on which, at variable points, 

 might have originated new systems of waves of the second order, of 

 less amplitude. S. paidsoni at one extremity, S. pavlsorio'ides at the 

 other, would represent such systems, turning aside more or less from 

 the wave of the first order, to continue the comparison, being able 

 even to substitute themselves for it and to efface it. On these would 

 be produced, by the same hypothetical mechanism, waves of the third 

 order, of still shorter amplitude, as, for examples, the races or sub- 

 species with trinomial appellations Avhich are attached so obviously 

 and so closely to S. apioceros, to S. townscndi, to S. mimts^ and to 

 S. herricki. The comparison permits us even to imagine that the 

 characters served at first to distinguish species, and that as the waves 

 spread and multiplied they changed their original valuation and 

 became characters of groups, and even generic characters. 



In order to complete the hypothesis, one might speak of the " peb- 

 ble ■'' which, falling on the summit of a wave of great amplitude, 

 might have given rise to a new system of vibrations, otherwise called 

 a new form. If one seeks to represent the one or the other of the two 

 ])ossible mechanisms, insensible '' fluctuations " or sudden " muta- 

 tions," one encounters the same impossibility of knowing. It is easy 

 to see at a glance that the two modes do not exclude each other, that 

 they are even very near to overlapping, provided Ave admit an ampli- 

 tude small enough for effectual variations. There are perhaps some 

 zoological groups which behave in a different manner from this point 

 of view. Each molt of an arthropod is a " mutation," while a verte- 

 brate " fluctuates " in order to attain its adult characters. According 

 to Professor Bouvier, Avho has in such a masterly manner demonstra- 

 ted the reality of mutations amoiig the Atyidaj and their great ampli- 

 tude, it would not be surprising if one found among other Crustacea 

 analogous exami^les. 



I think I can say that the Synalpheids at the present time show 

 nothing similar. I have examined, drawn, and measured all the 

 specimens of which I speak, excepting in the cases where the species 

 comprised several hundreds or more than a thousand specimens, 

 which for want of time I have only examined. The details which 

 can be referred to the facts of mutation by their unusual presence in 

 a series of specimens appear to be very few in number and without 

 special importance. For example, first, one of the specimens of S. 

 apioceros sanjosei has no spine on the anterior border of the wrist, 

 which fact permits of no hesitation in its determination ; second, one 



