aquatic JLitt 



173 



plant food, and in such circumstances it 

 thrived exceedingly well, and attained 

 a large size. 



Turning to the subject of thread spin- 

 ning, this can be observed and studied 

 with certain success if a large aquarium, 

 as previously described, is used. A self- 

 supporting vessel is essential, as the 

 water must not be disturbed, and the 

 growing plants must be in sufficient pro- 

 fusion to keep the water from becoming 

 foul with a small population of a hun- 

 dred or more adults. When the snails 

 have settled down, put in one large piece 

 of meat, more than is likely to be con- 

 sumed under two or three days, or renew 

 in exactly the same place without dis- 

 turbing the plants. Soon a vertical thread 

 will be seen reaching from bottom to top 

 and probably more or less attached at 

 intervals, to some upright leaf of Val- 

 lisneria. This thread will be observed to 

 gradually thicken as each snail in passing 

 along it adds its contribution of slimy 

 matter, and in quite a short time a rope 

 of respectable proportions is formed, 

 leading from the unconsumed meat to 

 the surface of the water, where many 

 ramifications will be found. This rope 

 sometimes becomes thicker than the 

 thumb of a man. There will be a con- 

 stant procession of snails up and down 

 the rope, and it is interesting to watch a 

 snail leisurely travelling on the surface 

 come into contact with one of the surface 

 ramification lines. In an instant, the 

 sluggish creature becomes alert and 

 quickens its pace. As far as I have been 

 able to judge there is never a mistake as 

 to the direction, and in a little time the 

 snail reaches the thick vertical rope and 

 commences its descent. There is much 

 interest centred here, as in a dense colony 

 many snails may be on the rope, and a 

 descending snail will not give way to an 

 ascending one. The hungry snail clings 



tenaciously to the guiding line, and the 

 repleted snail must give way. As the 

 rope is usually somewhat irregular, and 

 one side more or less attached to plants, 

 there are places which offer a limited 

 traveling surface, and only one snail can 

 be in possession. When the conditions 

 are ideal for observation, and the travel- 

 lers many, much amusement will reward 

 the observer. 



Anyone who has read Fabre on the 

 processionary caterpillar will remember 

 he describes how these creatures live in 

 large numbers in a common dwelling- 

 house, and on leaving which, for feeding 

 purposes, spin a thin line of silk. Each 

 caterpillar in the procession adds its line 

 to the existing one until it branches off 

 on its own account, and these lines are 

 used for the purpose of finding the way 

 back home, just as a cord or rope would 

 be used in the exploration of an intricate 

 cave. There seems to be a curious re- 

 semblance of methods of snail and cater- 

 pillar, and this is the most remarkable 

 seeing that a snail after a good meal, 

 puts up with all sorts of annoyances from 

 descending snails rather than leave the 

 guiding line, although it has the power 

 to float to the surface. Planorbis Cor- 

 nells, as is well known, can rise to the 

 surface from the bottom like a cork, or 

 sink like a stone, and it apparently has 

 considerable control over the rate of fall 

 and rise. In a deep aquarium a falling 

 snail will frequently retard its progress 

 very perceptibly as it nears the bottom, 

 and a rising snail will often carry a 

 piece of meat more than its own weight, 

 without any visible difference to the 

 normal rate of ascension, which shows 

 there must be a considerable latitude of 

 power. I have never been able to wit- 

 ness, when there has been no suspicion 

 of interference, a snail voluntarily fall 

 to the bottom, and ascend to the surface 



