The prolonged examination alarmed the snail, and it hud now with- 

 drawn into its shell. George held the shell quietly in his hand to see 

 if the animal would not come out again. While we were waiting for 

 this, Professor Parker asked us to count the heart beats of the animal. 

 The shell was turned over and we observed a movement inside, to the 

 left of the spot where the outer lip meets the body whorl. We moistened 

 this spot a little and it became almost transparent, so that we could 

 plainly see the beating of the heart through the shell. We were told 

 that the heart was composed of the ventricle and the auricle, the former 

 lying behind the latter. The pulsations were from right to left, the 

 auricle seeming to push the ventricle at every pulsation. We now 

 tried to count the number of pulsations in a minute. Harry held the 

 watch while the rest of us counted. We found the number to be fifty. 

 We then tried another snail to see if the number of pulsations were 

 the same. Again we counted and this time the number was sixty-one. 

 Professor Parker told us that the number of pulsations of the heart 

 varied greatly, and that if we had the time to examine a large num- 

 ber of specimens, the number would be found to range from forty-eight 

 to one hundred and six, the latter number being that of very young 

 animals. 



Not all of the snails which lived in the old log were as large as the 

 white-lipped snail, some being very minute. While pulling off the 

 rotten bark near one end of the log, Howard found quite a colony 

 of the little Pupa shells. It took sharp eyes to detect 

 them, for they were not larger than very small seeds, 

 and lay very close to the under surface of the bark. 

 With our pair of tweezers, we picked up a number 

 of the little fellows, some of which were put into 

 a small vial filled with alcohol, so that they would 

 not dry up or stick to the sides of the bottle when 

 dead. A few, we placed alive in a vial for study 

 when we returned home. We examined one of the 

 little specs with a hand lens and it appeared like the shell in the 

 picture. The whorls were rounded, the spire quite long, and the aper- 

 ture was modified by six teeth, or projections. When we saw the aper- 

 ture so obstructed by teeth we wondered how the 

 animal was able to crawl in and out. Professor 

 Parker then said that in tropical countries, there 

 live certain species of snails whose apertures are so 

 contracted by teeth that scarcely any room is left for 

 the animal. 



Shell of Pupa, a mi- 

 nute land snail. The 

 crossed lines at the 

 right of the figure in- 

 dicate the actual size 

 of the shell. (Binney.) 



W!MI 



Aperture of Pupa 

 shell, greatly magni- 

 fied. (Binney.) 



29 



