MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



387 



TABLK n Continued. 



{Locality: Nassau, N. 1'., Bahama Islands.] 



VII. THE CAUSES AND SIGNIFICANCE OF VARIATION IN ALPHEUS SAULCYI. 



If we consider Nos. 1 or 2 of Table 1 as representing the nearest approach to the mean of the 

 species, Nos. 5 to 15 must stand for individuals which have fluctuated farthest from the mean. 



The individuals given in the table were chosen without reference to sex, yet it appears that 

 nearly two-thirds of the number are males. In examining a larger collection of these aberrant 

 forms 1 find a still greater percentage of males. There can be little doubt that in those cases the 

 males are in the excess, although I have not tested this point carefully. It is also evident from 

 observation and detailed measurements that the average size of these abnormal individuals is less 

 than one-half that of the brevicarpus type. The brown sponges teem with a population of under- 

 sized forms, nearly all of which are aberraut, and none of those which were examined exceeded 

 the length of 17.5 mm , which is considerably less than the average for the type. 



How far are these variations individualistic and how far are they confined to the race or 

 species as a whole! In other words, is the individual plastic, departing from the standard of the 

 species and becoming different at different periods of its life, or do individuals deviate from the 

 mean of the species, each along its own line ? Further, are the variations congenital ? While we 



