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THE AMERICAN NATURALIST [Vol. XLV 



August 19, 1909, a minute ancyloid specimen was taken, 

 and another August 24. September 26 six ancyloids 

 were visible at one time, but were not disturbed. It was 

 noticed that the ancyloids came out in sight on the walls 

 of the jar more freely on cloudy than sunny days. 



This jar, December, 1909, contains a dense and vigor- 

 ous growth of Anacharis, also plenty of fresh-water 

 alga\ It stands in the factory room subject to the fall 

 of factory dust, and to the changes of temperature in 

 the room. When the room gets unusually cold the 

 ancyloids mostly retire out of sight, temporarily. De- 

 cember 9, 1909, two specimens with the third stage of 

 the shell partly grown were taken near the top of the jar. 

 A sudden spell of unusually cold weather having begun 

 two nights previous may account for the ancyloids hav- 

 ing gone, as they did, into hiding, but it was somewhat 

 surprising that the more nearly mature form had not 

 also hidden. 



The 8 X 6-inch Jar.— This had sand on the bottom and 

 was planted with Anacharis from the larger jar, carry- 

 ing with it Ancylus, Gundlachia and Piano rbis parvus 

 in the summer of 1908. The following winter, having 

 nothing but sand and water to live on, the vegetation had 

 become rather attenuated and feeble looking. The ancy- 

 loids were few and perhaps not more than half as large 

 as those in the larger jar. January 19, 1909, two or three 

 immature septate specimens were taken from this jar, 

 and February 10 one about half grown. Very few ancy- 

 loids were seen about this time in this jar. February 11 

 two immature septate specimens were taken, being all 

 of either form which were at that time visible. Feb- 

 ruary 24, 1909, for the first time since the eleventh, a 

 small ancyloid was noticed. On the twenty- seventh one 

 moderate-sized but fully septate individual was taken 

 and one ancyloid seen. Another septate was taken 

 March 8, and March 11-13 a solitary ancyloid was 

 noticed. 



Fearing that there was not enough stock in the jar to 



