60 JEAN DAWSON 



spinning for any length of time, other things being equal. Food 

 and spinning are very closely correlated, and snails are nearly 

 always seen spinning very actively either upon their food or 

 in its immediate vicinity. A snail that had not been spinning 

 was caused to spin by the following device : A tube, the ends 

 of which were closed with fine wire netting, was placed in 

 the aquarium with snails. The tube was filled with the pulp 

 of apple, only the juice of which penetrated into the surrounding 

 water. Some snails were soon attracted and presently began 

 to spin before the wire netting. This experiment is significant 

 in that the snails did not eat the food, but the flow of their 

 mucus was affected in much the same way that our saliva is 

 stimulated by the odors of attractive food. 



It is not known why spinning in Physa accompanies feeding. 

 The mucus as shown above is much thinner shortly after food 

 is taken and this may have an important bearing on the initial 

 act of spinning, namely, the detachment of the snail from the 

 substratum. Hart's (1862-3) remarks on the effect of food upon 

 the spinning of the land pulmonate Li max arhorum are inter- 

 esting in this connection. " It has also been observed that 

 when this species is gorged with food, its slime is thin and watery 

 and unable to sustain its weight, but after the process of diges- 

 tion has been performed, the mucus again becomes thick and 

 tenacious." From this it is seen that the mucus when spinning 

 takes place is much more tenacious in Helix arhorum than in 

 Physa. The thread of the land pulmonate is spun down from 

 the edge of a solid through the air, while the water snail spins 

 its thread usually from the surface of a solid up through the 

 water. The snail Helix arhorum is much heavier than Physa 

 and would of necessity require a stronger thread. It also 

 has a reaction above mentioned that Physa has not, i. e., the 

 crawling off from the edge of a solid instead of keeping its head 

 in and following the surfaces. It is thus seen that the initial 

 act of Limax arhorum in spinning is to move straight oft" from 

 a solid while the foot of Physa must be loosened first from the 

 substratum and it is probable that the thinning of the mucus 

 makes this possible. 



2. General activity affects spinning. The general tonus mod- 

 ifies spinning in that it affects food taking and the general 

 activity of the animal. Light may be shown to accelerate 



