§2] 



EFFECT OF EXTENT OF MEDIUM ON SIZE 



477 



FiQ. 135. — Two individuals of Limnaea stagnalis, which have lived from May, 1891, to 

 January, 1892, in two flasks nearly alike in respect to surface and volume of water. 

 In the one case (shell at left) the flask, enclosing 500 cc. of air, was sealed ; in the 

 other case (shell at right) the flask remained unsealed throughout the 8 months 

 of experimentation. 

 (From DE Tarignt, 

 '94.) 



Fig. 136. — Limnsea auri- 

 cularis, reared in dif- 

 ferent masses of water 

 having the same sur- 

 faces but different 

 volumes. The speci- 

 mens, taken in order 

 from left to right, 

 were reared in vessels 

 having surface areas 

 of 100, 200, 400, and 

 500 cc. respectively. 

 Experiments extended 

 from 15 November to 

 6 April. (From de 

 Varigny, '94.) 



Fig. 137. — Limnaja stag- 

 nalis. The individual 

 at the left lived from 

 18 November to 20 

 April in a liter of 

 water having a sur- 

 face of only 2 era. diam- 

 eter ; that at the right 

 lived during the same 

 period in an equal vol- 

 ume of water having 

 a surface of 18 cm. 

 diameter. (From db 

 Vakignt, '94.) 



Fig. 138. — The Limnaea 

 stagnalis at the left 

 lived from 21 Novem- 

 ber to 6 January in 

 1350 cc. of water hav- 

 ing a surface of 3.5 cm. 

 diameter ; that at the 

 left, somewhat larger, 

 lived during this pe- 

 riod in 600 cc. of water having a surface of 16 cm. diameter. (From de Varigny, 

 '94.) 



Fig. 139. — Limnsea 1 lived from 18 November to 5 April in a glass without a bottom 

 (capacity 250 cc), suspended in the beaker (capacity 4200 cc), in which 2 lived. 

 Limnsea 3 lived from 20 November to 7 February in a tube, suspended in a vessel 

 in which 4 was reared. Limnsea 5 lived from 9 April to 24 June in a tube, sus- 

 pended in the vessel in which 6 lived. (From de Vakignt, '94.) 



139 



