1892.] Proceedings of Scientific Societies. 87 



noteworthy of these is the series of observations made b\ - 

 witsch, on the effect of the degree of saltness of the water in which 

 certain animals live upon the form of the body. The form experi- 

 mented upon was a rather lowly organized crustacean, known m Artt- 

 mia salina, which normally lives in water of a moderate decree of sa- 

 linity. By gradually increasing the saltness of the water, in the cour-e 

 of several generations, the animals assumed the characteristic- ..f an 

 entirely different species, known as A. muhlhatiscnii. By gradually 

 diluting the moderately salt water with fresh water until it become! 

 practically fresh, the A. salina gradually assumed structural eharacier- 

 istics which rendered it necessary to refer the forms thus obtained to an 

 entirely different genus, Branchipus. Here we have, apparently, a 

 very good case of the production of definite variations of form under 

 the influence of external conditions. 



A further study of the results, however, brought out some facts which 

 diminish the value of these observations for our present purposes. It 

 was shown that A. salina resembled an immature form of Branchi- 

 pus, while A. niuhlhao.iehii represents a stage which is passed over 

 in the immature life of both Branchipus and A. salina. In other 

 words, the effect of the salinity of the water was not to produce definite 

 variations of the body form, but to produce an acceleration of the ma- 

 turity of the reproductive elements, so that in the water of the greatest 

 degree of saltness the animals became mature, while the body form was 

 still in a larval condition. 



A few cases have, however, come under my observation which have 

 bearing on the subject. Among the Isopod Crustacea of our coast is a 

 form, Jaera, which presents a great variety of coloration ; all the varia- 

 tions may however, be reduced to two types, one in which the coloration 

 is uniformly distributed, and the other in which the pigment is arranged 

 in transverse bands. Within these limits the variations are innumer- 

 able, but still the variations may be considered definite. A similar vari- 

 ability within definite limits has been described in another Isopod. In 

 certain sea anemones, as well as in certain caterpillars, the color ap- 

 peared to be due to environment purely. 



Comparison of processes of variation to vicarious substitutions 

 which occur in the more complicated silicates of the mineral worM was 

 made. The number of substitutions is limited, but within these limits 

 the amount of variation is practically indefinite, if not infinity 



Vbetebkated Animals.— Professor Allen next spoke on " \ ana- 

 tions in Vertebrated Animals. He confined his paper to variations 



