438 



ROBERT W. HEGNER 



SPECIMENS WITH BENT, OVAL SHELLS 



Among the specimens of Arcella polypora that were collected 

 at Cold Spring Harbor dm-ing the summer of 1918 were many 

 with a shell that was oval in outline and contained an oval mouth 

 opening and at the same time was bent slightly as indicated in 

 figure 7. Most of these were obtained from duck weed taken 

 from a small pond that was gradually drying up, but others were 

 found in a small lake. Leidy (79, pi. XXVIII, figs. 36 and 37) 

 figures shells similar to these. A number of specimens were 

 isolated and their progeny examined. The offspring of the first 

 generation were either circular in outline or nearly so and almost 



Fig. 6 Arcella dentata. Camera-lucida sketches (X 450) of three of the 

 spines belonging, respectively, to normal specimens (A, 1 and B, 1) and to the 

 first offspring produced bv them when subjected to low temperature (A, 2 and 

 B, 2). 



flat, and those of later generations were entirely normal when 

 reared under laboratory conditions. A few measurements are 

 given below. 



A large number of specimens were placed in Syracuse watch- 

 glasses and examined every day for a week. Many offspring 

 were produced by them, but in every case they were quite normal 

 or nearly so. Since the descendants of these bent, oval speci- 



