is simply a straight tube. In the young animal, the shell is spiral. Some 

 land shells, called Cylindrella, have been seen to voluntarily break off the 

 dead apex by hitting it against a stone. 



As it was now getting late, the collecting outfits were packed, and 

 we started to walk to the car line, which was about a mile distant. On 

 the way, we passed a small stream on one side of the road which was 

 literally filled with decaying vegetable matter, and across from it on the 

 other side of the road was a small pond fairly black with fine, impalpa- 

 ble mud held in suspension in the water. George began to examine 

 these places in the hope of 

 finding a few more snails, but 

 he was told by the Professor 

 that mollusks could not and 

 would not inhabit water in 

 such a condition. In the case 

 of the first stream, the de- 

 caying vegetation caused the 

 presence of carbonic acid gas, 

 which was inimical to the life of the snail ; and in the pond, the fine mud 

 interfered with the breathing of the mollusks. It was also learned that 

 a stream with a very rapid current and a bottom composed of crystal- 

 line gravel was not well adapted to the life of fresh-water snails. Such 

 snails as Physa, pond snails, and apple snails- love a still pond or sluggish 

 stream, in which the bottom is more or less muddy. 



On our way home in the cars, we amateur conchologists plied Pro- 

 fessor Parker with questions about fresh-water snails. Observing that 

 we were thoroughly interested, he suggested that we visit the museum 

 with him the following Saturday, and study the different types of this 

 class of mollusks. To this, all gladly assented. 



Apple snail, Vivipara intertexta. Animal and shell 

 viewed from above and in front. Left figure', female; 

 right figure, male. (Binney.) 



17 



