314 THE CHICAGO ACADEMY OF SCIENCES. 
water as cold as the freezing point, and may be observed in 
winter gliding along the bottom of a pond when the surface is 
frozen. The eggs are deposited on stones, the under side of 
sticks, etc., and are composed of large, glairy, transparent 
masses. 
Several Phys@ kept in captivity laid four egg masses on 
April 23, 1897. These measured 20 by 4 mill., and contained 
from 130 to 200 eggs (one membrane 130, one 160 and one 200, 
Fig. 112). On April 24, ten additional egg masses were laid, 
the jar containing fifteen individuals. On June 3, in the after- 
noon, the writer noticed a number of young in a jar containing 
egg masses probably deposited in the latter part of April. The 
young were half a mill. in length, vitreous in appearance and 
perfectly transparent. They were very lively, crawling about 
the jar and eating voraciously. The heart pulsated one hun- 
: 
b 
Fie. 112. 
_Egg-mass of PHySA GYRINA Say. (Original.) a, egg-mass, showing 
position of eggs in envelope; b, single egg, much enlarged, showing posi- 
tion of rotating embryo. 
dred and twenty times per minute. On June Is, the young 
had increased to 1 mill. in length. Unfortunately, about a 
week later the whole lot died, so no further notes could be 
taken. - 
Physa gyrina is by far the most common species of the 
genus (I might say of any genus) found in the area, and has 
been found in all parts of the region. It was at first confused 
with eéerostropha, but that species has a smooth shell (see 
above) and is not found in any numbers in the area; it is very 
probable that Heferostropha is not found west of the Mississippi 
River, and the quotations of this species from western locali- 
ties were probably founded on gyrina, sayit, gabbi, integra, etc. 
