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 Physce 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 



FIG. 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 15, the young 

 had increased to I 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 heterostropha, but' that species has a smooth shell (see 

 above) and is not found in any numbers in the area; it is very 

 probable \.\\3.\.heterostropha'\s not found west of the Mississippi 

 River, and the quotations of this species from western locali- 

 ties were probably founded on gyrina, sayii, gabbi, Integra, etc. 



