LYMNZIDZ OF NORTH AMERICA. 47 
its fringe of cilia and its locomotor function (see plate II, figures C, 
13 ae 
The young Lymnea, just before it leaves the shell, is an interest- 
ing object, especially when viewed with a lower power (about Y% inch 
objective) by the aid of which its spiral journeyings inside the egg 
may be observed (plate IJ, figure B). The shells at this time consist 
of a trifle less than two whorls, which are flat and helix-like, quite 
‘unlike the long-spired shell of the mature animal.? The eggs of Lym- 
na are easily obtained and the development of the embryo may be 
plainly seen and studied with ordinary powers of a compound micro- 
scope. Much good work may be done by anyone who will compare the 
development of some of the common species. 
The effect of different colored lights and also the different den- 
sities of light on the developing eggs of Lymnza has been interest- 
ingly shown in a series of experiments by E. Young’ who records 
the following variations in the time of hatching: In violet light, 17 
days; in blue light, 19 days; in yellow light, 25 days; in white light, 
27 days; in red light, 36 days; and in darkness, 33 days. 
k. EXPERIMENTS. 
The genus Lymnza has been frequently used in conducting ex- 
periments relative to the animal’s power of resisting changing condi- 
tions of the environment. Whitfield’s experiments on Bulimnea 
megasoma‘ are well known. Specimens of this large Lymnaa were 
confined in an aquarium of small size and were bred to the fourth 
generation. Each succeeding generation was smaller than the one 
preceding, the last or fourth generation producing a shell about half 
the size of the first generation, with an elongated spire and generally 
narrow form, quite unlike the robust form of typical megasoma. Whit- 
field concluded that the volume of water bore a very close relation to 
the size and perfection of the shell. Certain interesting changes were 
also noted in the organs of the animal, such as the loss of the male 
sexual organs and a notable reduction in the size of the digestive 
glands. This degeneration is thought by Dall to be due rather to a 
concentration of salts, as the evaporated water was replenished with- 
out emptying the residual supply, causing an excess of salts to accumu- 
late. 
iSee Lankester, Quart. Journ. Micr. Soc., Vol. XIV, p. 365, 1874, for an 
extended account of the development of Lymnaea. 
: 2See an interesting account on this subject by Jabez Hogg, in Trans, 
Micr, Soc. London, II, p. 91, 1854. 
3Arch. Zool. Exper., VII, pp. 273, 274. 
4Bull. Amer. Mus. Nat. Hist., I, p. 29, 1881. 
