1908.] NATURAL SCIEXCES OF PHILADELPHIA. 413 



phia. It is not quite as abundant, perhaps, as is Physa; yet, except 

 when the ponds are frozen in the winter, is easily procured. A fact 

 of the greatest importance is that eggs are laid throughout the winter, 

 and that these eggs ordinarily develop with slight mortality. The 

 Lymmea on which the following experiments were performed was 

 identified by Dr. H. A. Pilsbry as Lymncea columella Say. This is the 

 most common Lymncea in the neighborhood of Philadelphia. The 

 specimens were procured in certain ponds in Fairmount Park, in a 

 stream near Bryn Mawr, and in the Vivarium of the University of 

 Pennsylvania; the latter had come from an unknown source. 



The numJDer of eggs laid at one time by Lymncea columella may vary 

 between one egg and ninety. The egg is, as in the case of other Basiom- 

 matophora, imbedded in an albuminous food material, all of which is 

 enclosed by a membrane. This membrane is in turn imbedded in a 

 shmy jelly in which lie the other eggs, laid at the same time. This 

 slimy jelly is again surrounded by an outer layer of jelly, which is 

 quite tough when compared to that matrix which holds the eggs. This 

 tough jelly is thick on the free side, but thin where it cements the eggs 

 to the substratum. In the act of hatching the young snail, which 

 crawls around inside of the membrane, finds its way into the soft jelly 

 mass. After spending a day or two eating this substance, it finally 

 ruptures the wall of tough jelly and escapes. In this jelly mass the 

 eggs are usually placed in three rows. Although the number of eggs 

 may vary greatly, yet in the winter time the average number is about 

 twenty. When adult snails, as soon as the ice is off the ponds in the 

 spring, are brought into the laboratory, they lay the largest number 

 of eggs in a capsule. This fact will be discussed later. 



To shed some light on the behavior of the snail after hatching, an egg 

 case containing four young was placed in a dish of water and the posi- 

 tions of the snails after hatching plotted at intervals of five minutes 

 for a period of forty-four hours. From the data gathered in this 

 manner the following generalizations were made: — 



1. Although on hatching the lung contained no air, yet 95 minutes, 

 50 minutes, 110 minutes and 60 minutes respectively were consumed 

 by the different snails in reaching the surface of the water. One snail 

 captured an air bubble before it left the egg case. 



2. The movements of snails, previous to their reaching the surface, 

 were more or less at random, and they paid very little attention to the 

 direction of the diffused light in which the experiment was started. 

 However, on first reaching the edge of the dish they, in every case, 

 crawled up to the surface. The snail that captured the air bubble 



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