C. L. Walton 
247 
L. truncatula placed upon mud containing much organic matter, 
and taken from a pond not inhabited by these mollusca, left this mud 
persistently and climbed the sides of the dish. If placed on a sod from 
a stream margin and supplied with clear water from their own stream 
they crawl out, or up the grass stems and these fix themselves and die 
of drought; but should diatomaceous mud be added, they will remain 
upon it and live for considerable periods, sometimes for months, pro¬ 
vided a suitable supply of food and water is maintained 1 . 
Growth rates vary considerably, but, although continuous, are 
certainly slower in winter than during the more favourable months. 
In the majority of cases it is evident that L. truncatula hatched in the 
autumn does not reach a length of 5 mm. until the following Feb. or 
March, while those hatched in spring make very rapid growth and 
attain 5 mm. in eight or nine weeks. 
j/ 
Movements and Migrations. 
Mention has been made already of a ditch in which L. truncatula 
occupied the sides, the centre being too soft for that species. L.;peregra 
was very abundant in a stream and pond not far away and in March, 
1914, this stream dried and I removed 80 specimens to the ditch in order 
to prove if possible that L. peregra would live under the conditions 
which I regarded as favourable to it. This batch was placed in one 
spot in order to watch any migration that might take place. On April 
28th, another 50 were added from the pond, making 130 in all. By 
May 1st, many had disappeared, possibly owing to the depredations of 
water rats, since signs of these animals were numerous about the spot. 
The ditch became very low during the summer and by Oct. 23rd, some 
of the snails had spread down stream for a short distance. Just after 
this the ditch was cleaned out prior to the commencement of the autumn 
rains and on Jan. 28th, 1915, only one very large specimen could be 
found out of the original 130, while truncatula had completely dis¬ 
appeared. By Feb., 1916, L. peregra had become abundant and occupied 
40 feet of ditch below the original point of colonisation, but upstream 
they had extended as far as conditions were suitable, .being then arrested 
by a sharp increase of slope which caused the bed at that point to be 
scoured clear of mud. I have always found that peregra will advance 
against a current at a surprisingly rapid rate, averaging in one instance 
two yards per day. I have never noted any such habit in the case of 
truncatula. 
1 If placed upon soft L. peregra mud, L. truncatula crawl out if they can. 
