342 LAND AND FUESH-WATER SHELLS. 



The growth of the fresh- water Nerites would ap]>ear to be slow. 

 I kept a young individual of Neritina subsukata for seven months 

 in a bottle partly filled with rain-water, and supplied it with decay- 

 ing leaves for food which it used to eat. Its weight was 87 grains 

 both at the beginning and the end of the experiment, having only 

 varied half a grain during the whole time ; and its dimensions, as 

 determined by measurement, were unaltered. This species, when it 

 is first picked off* the rock, ejects a watery fluid with a powerful 

 musky odour, which eff'ect accompanies the closure of the shell by 

 the operciilwn. I kept some individuals of this species in rain-water, 

 containing varying proportions of lime-water, for about three months. 

 The lime-water was of the medicinal strength of the British Phar- 

 macopeia. I began with water containing 64 parts of rain-water 

 to one part of the lime-solution. By the end of the first month the 

 proportion was increased to 32 to 1 ; by the end of the second 

 month it was 16 to 1 ; towards the end of the third month the 

 Nerites, having lived for over three weeks in the last solution, began 

 to die; the survivors were placed in a solution containing the pro- 

 portion of 8 to 1, but this amount of the lime-solution proved too 

 much for them. It should be remarked that throughout the experi- 

 ment, the Nerites used to descend to the water to get their food just 

 as frequently as in the state of nature: they did not avoid the water ; 

 and after the experiment was over, there was no apparent altei-ation 

 in the appearance of the shells. These observations were made in 

 the north part of New Zealand during the latter part of the summer 

 and the beginning of the autumn, a circumstance which may parti- 

 ally explain the death of the shells. The temperature there was 

 about 20° below the temperature they are accustomed to in the 

 Solomon Islands ; this difference is of interest when it is remembered 

 that Neritince are mostly found in the streams of tropical regions ; 

 and I may, therefore, infer that this species is capable of adai)ting 

 itself to temperatures much lower than that to which it is accus- 

 tomed, since some individuals survived the voyage to New Zealand 

 from the Solomon Islands and lived in the climate of the former 

 region for three months under very unfavourable conditions. 



Professor Semper^ remarks that some NeritincB have the habit 

 of detaching themselves from rocks on the slightest touch, by this 

 means, as he considers, escaping the pursuit of their enemies. Some 

 of them, however, as I observed, detach themselves spontaneously 



1 Ibi.l, p. 210. 



