48 .THE CHICAGO ACADEMY OF SCIENCES. 



Several European zoologists have experimented in the same man- 

 ner, producing very interesting results. Thus, Semper 1 bred speci- 

 mens of Lymncea stagnalis from the same egg mass and placed them 

 in aquaria of different volume varying from 100 to 2000 cubic centi- 

 meters. All of the essential conditions of life were kept as uniform as 

 possible, especially the food supply. At the end of sixty-five days the 

 specimens from the 100 c. c. aquarium measured 6 mill, in length, those 

 from the 250 c. c. aquarium measured 9 mill, in length, while those 

 from the largest aquarium, 2000 c. c. were 18 mill. long. Semper con- 

 cluded from these experiments that the size of the shell varied in 

 proportion to the volume of water, and that the effect was the same 

 whether one or several individuals were confined in the same aquarium. 

 The factor of temperature was accidentally shown in Semper's experi- 

 ments; when the temperature fell to 55. The aquaria were placed 

 near a window through which the sun shone, raising the temperature 

 of the smaller aquaria but having no effect upon the larger aquarium. 

 The consequence was that the individuals in the 2000 c. c. vessel, 

 which should have been 10 mill, in length when 25 days old, were but 

 little longer than those individuals which were contained in the smaller 

 aquaria, the water of which had been warmed by the rays of the sun. 



De Varigny 2 experimented in a similar manner by breeding snails 

 in aquaria containing equal volumes of water, but with varying surface 

 areas. The result was that the largest individuals were produced in 

 those vessels having the greatest surface areas. De Varigny was led 

 to the conclusion from the result of these experiments, that the chief 

 factor in growth was an extensive surface area which permitted ex- 

 tended locomotion. 



Willem, 3 having in mind the experiments of Semper and De Var- 

 igny, carried on two distinct sets of experiments. The first experi- 

 ment consisted of two similar aquaria, one filled with stagnant water 

 and the other with water into which a constant air stream was intro- 

 duced. The result after three or four months was that the snails in 

 the aeriated jars were very much larger than those in the aquarium 

 containing stagnant water. In the second experiment two vessels of 

 different sizes were used, the surface areas of which bore the ratio 

 of 8 to 1, the volumes of water being respectively 3110 and 310 c. c. 

 An equal amount of air was kept passing through either jar, and at 

 the end of three months the snails in the larger vessel were of the 



iArbeiten Zool.-Zoot. Inst., I, p. 137, 1874. 

 2 Journ. Anat. Physiol., XXV, pp.147-188, 1894. 

 3Bull. Acad. Roy. Sci. Brussels, XXXII, p. 566. 



