i68 The Irish Naturalist. December. 



On the nth July, fourteen days after the eggs laid in 

 captivity had been placed in the petrie-dish, the dish was 

 examined. Many of the eggs were found to be shrivelled 

 up. They were evidently " addled." Others were still 

 quite plump, and one of these being carefully opened was 

 found to contain a young snail enclosed in a transparent, 

 colourless shell. This unhatched juvenile was already pro- 

 vided with a distinct radula or lingual ribbon, having a 

 total of 240 teeth ranged in 25 rows, varying from 4 to 16 

 teeth in the row, with the median tooth well developed in 

 the wider rows. In a well-grown adult H. aspera as many 

 as 15,000 teeth have been counted in the radula. 



Three days later, on the 14th July, another plump egg 

 was taken from the mould in the petrie dish and for facihty 

 of examination was fully immersed in fresh water in a large 

 watch-glass. Soon after immersion the tip of the foot was 

 extruded from the e^^, and in little more than three hours the 

 animal had completely worked its way out. The upper 

 tentacles w^ere a beautiful pale violet colour, and the beating 

 of the heart could be plainly seen through the transparent 

 shell. The beats varied from 40 to 50 per minute, and the 

 young snail lived fully immersed for 29 hours. One might 

 be tempted to find in this sub-aqueous vitality of a juvenile 

 pulmonate or air-breathing mollusc an illustration of the 

 recapitulation theory, in which the early stages of an 

 organism are reminiscent of its remote ancestry ; for it 

 has been suggested that the forefathers of the land snails 

 are to be found in the marine nudibranchs. But this would 

 be too daring an exercise of the scientific imagination, all 

 the more so as this capacity for a somewhat lengthened sub- 

 aqueous existence is shared by the adult. 



On the i6th July, just eighteen days after the laying of 

 the eggs, 25 young snails were found hatched out and 

 buried in the mould, which adhered to the copious mucus 

 of the foot so as to make it by no means easy to distinguish 

 the animal. The following day 20 others issued from the egg, 

 making a total of 45 successfully hatched out of 75 placed in 

 the mould in the petrie-dish on the 28th June. The young 

 snails were so lively that it was found necessary to keep 



