ENVIRONMENT ON ARCELLA 437 



One of the progeny was irregular in shape and another was 

 without definite spines. It is evident from the results that alcohol 

 is injurious to these organisms, although they are able to with- 

 stand the presence of a considerable amount for a long period. 



TEMPERATURE 



A number of specimens of Arcella dentata were collected on 

 December 27, 1917, from pond weeds under a layer of ice eight 

 inches thick. Many of these had no well-developed spines, but 



Fig. 5 Arcella dentata. Family 15. Camera-lucida sketches (X 207) 

 showing: 



A = the original progenitor with twelve spines and diameter of 27 units. 



B = the first offspring after A was placed in a solution of one drop of sodium 

 silicate to 100 cc. of normal medium. 



C = the first offspring of B, after B had produced two offsprings while in 

 sodium silicate solution and was then transferred to normal medium. 



D = the first offspring of C while C was in normal medium. 



their progeny, when reared under laboratory conditions, exhibited 

 a complete set of fully formed spines. This suggested that per- 

 haps the low temperature might have been responsible for the 

 lack of spines in the 'wild' parents. Several experiments were 

 begun to test this hypothesis, and although they were not ex- 

 tensive they indicated that length of spine and temperature may 

 be correlated since, as shown in figure 6, the spines of offspring 

 reared at a temperature of about 10°C. are smaller than those of 

 their parents which were reared at room temperature. 



THE JOURNAL OP EXPERIMENTAL ZOOLOGY, VOL. 29, NO. 3 



