PEARL ON A HABIT OF THE SLUG, AGRIOLIMAX. 75 



A CURIOUS HAUIT OF THE SLUG, AOiaoJ.LMAX. 



I'.Y ItAY.MOXl) I'KAUr.. 



On December 11, 1000, while exaiuinijiy' some collections which had 

 been bioiight into the laboiatorv two days previously, I noticed a speci- 

 men of the common sluj^ Af/riolinid.r (■aiiiiiis-tris Bhniey, crawling on 

 the side of the aquarium jar behtw the surface of the water. AVlieu 

 first observed tiie animal was about lw<» inches below the surface and 

 Avas crawling- upwards. The mateiial, Mliich was collected in the Huron 

 river just below the dam at Ann Arbor, consisted principally of Gera- 

 1oi)hi/lli()ii and FAodcu. When the plants were torn loose from the bottom 

 in making the collection a considerable amount of mud had been taken 

 along with them, so that there were from two or three inches of mud 

 in the bottom of the, aquarium jar. 



The slug was removed from the aquarium immediately and placed in 

 a dish of fresh tap water. On the bottom of this dish it crawled about 

 at a rate slightly faster than the normal. The tentacles were not as 

 much extended as is the case under normal conditions, but this was the 

 only noticeable difference in the appearance of the slug in water from 

 that in air. It is noteworthy, however, that while in the water in the 

 warm room (temperature about 21° C) the animal never stopped crawl- 

 ing. On the contrary, it would keep in active movement until it had 

 reached the side of the dish and crawled up above the surface of the 

 Avater; then, having reached the air, it would soon come to rest. It 

 may be mentioned here in passing that it was possible, by preventing 

 the slug from passing out into the air when it reached the surface, to 

 induce it to crawl on the under side of the suiface film. It was able to 

 support itself on the film, and to progress slowly in the same way that 

 a water form like Plujiia or Limnum does. 



Experiments w'ere performed to test the effect of temperature on the 

 behavior of this specimen. As has already been stated, it would not 

 stay in the water in a room at ordinary teuiperature or a little above, 

 but, under these conditions, crawled out into the air as soon as possible. 

 To determine how it would behave in a low temperature it Avas first 

 placed in the Avater at the bottom of the dish and then the dish Avas 

 l)ut out in the open air and left for an hour. At the end of this time 

 the temperature of the Avater Avas -f- 2° C. The animal Avas very much 

 contracted; the tentacles w«^re <omi)letely drawn in. and the whole 

 body very much shoiteued. It Avas (piiet and had moved only about tAVt> 

 inches since the beginning of (he (experiment. At the end of the hour 

 the dish was taken into the \\arm room and in ten minutes the slug 

 began to move again. The body and tentacles expanded and Ihe animal 

 craAvled out of the Avater. 



After an inteival of an half hour the dish Avas again \m\ out of doors, 

 but with the slug on the side of the dish above the water. The obser- 

 vations at the beginning of this ('Xi>eriment Avei-e interrupted so that 

 I am unable to tell ijrccisdy what hajtpened. Init at the end of fifteen 



