C. L. Walton 
9 
o/ 
Effects of Drought upon the Ova. 
In no case of drying, natural or artificial, was L. truncatula ever seen 
. to make any attempt either to burrow, to hide, or to follow the retreat¬ 
ing waters, and was never found to have crawled voluntarily more than 
a few inches away from water. Prof. Thomas mentions a most important 
factor; namely grass. In my experience the presence of grass plays 
a great part not only in determining the period of survival of L. trun¬ 
catula, but in governing largely the certainty and degree of recovery of 
the snail population upon the return of water after a drought. In 
other words grass acts as does a “mulch” in gardening practice in the 
preservation of moisture; and further, prevents to a large extent the 
removal of the surface layers of the ditch as dust by the wind, which 
otherwise takes place to a very considerable extent in exposed situa¬ 
tions. 
The ova masses, when dry, are hardly visible upon leaf or stone. 
The whole having shrunk to a hard scale much resembling a drop of 
dried varnish. No matter how long these have been dried (experi¬ 
mentally) in all cases I have found their original form to be resumed 
within a few hours following replacement in water. 
Large numbers of snails of all ages and sizes were brought into the 
Laboratory from different localities and kept to observe at what size 
deposition of ova commenced. They were separated into lots allowing 
a difference of -5 mm. in length between each lot, and from these experi¬ 
ments it is concluded that L. truncatula becomes adult when a length of 
5 mm. is reached. 
It was found impossible (owing to accidents, etc.) to prove experi¬ 
mentally that drying of ova masses causes a prolongation of the hatching 
date after the return of moisture, but very numerous field observations 
point to this conclusion. Ditches, etc., that became dry, and remained 
so, for as long as three months, all became re-stocked with L. truncatula 
during the following spring. This occurred both in 1915 and 1916. 
The dates of re-appearance of young snails vary considerably and it is 
my opinion, judging from many such cases, that the longer the desicca¬ 
tion the fewer will be their number. 
The only spots that did not become re-populated in the spring of 
1916 were a few that had been thoroughly cleaned out, thus of course 
removing all ova. Even some of those cleaned out (but not thoroughly) 
were subsequently found to be inhabited in the following year, sometimes 
to my great surprise. In every case care was taken to ascertain whether 
