i9i8. CoLGAN. — Reproduction of the Common Snail. 169 



their travelling instinct within bounds by confining them 

 in a crystal chamber formed of two large watch glasses 

 placed edge to edge one over the other. A second brood 

 hatched out with me under similar treatment on the 8th 

 August, after 18 days' incubation, as in the case of the first 

 brood. ^ 



The shell of the freshly hatched snail had a diameter 

 of 4 mm. ; it was almost colourless, faintl}^ tinged with 

 3/ellow, but showing no signs of the characteristic blotchings 

 which have earned for the species the name aspersa. In 

 air, the heart in four specimens examined was found to 

 give 60 regular beats to the minute. One of these four 

 immersed in water had its heart-beats soon reduced from 

 60 to 45 per minute, showing a reduction of vitality by 

 change of element. The eyes, so obscure in the dark coloured 

 adult, were most conspicuous in the juvenile as black dots 

 on the translucent violet tentacles. The otocysts, or 

 chambers enclosing the otoliths or auditory granules, about 

 20 in number in each cyst, were clearly visible under a one- 

 sixth inch objective when the head of the animal was sub- 

 jected to gentle pressure. As one followed with fascinated 

 gaze the rapid tremulous oscillations of these ovate granules, 

 the very heart of the mystery of molluscan sensation seemed 

 to be laid bare. 



As soon as hatched the snails began to feed. The young 

 leaves of the Everlasting Pea were found to suit their taste 

 admirably. These they devoured greedily, though at long 

 intervals, stripping off the tender parenchyma from the 

 leaves until a band of green appearing through the trans- 

 parent shell showed that the juvenile w^as gorged. Growth 

 was on the whole rapid and especially so in that important 

 organ, the radula, on which a series of observations was 

 made with the results set out in the following table : — 



^ In the " Cambridge Natural History," vol. iii., p. 43, the Rev. A. H. 

 Cooke says that he succeeded in hatching out eggs of Helix aspersa, during 

 the very warm summer of 1893, in 17 days. It seems not improbable 

 that under conditions of steady heat and moisture the incubation period 

 may become shortened to 15 days. 



