No. 531] GUNDLACHIA AND ANCYLUS 



185 



continue the race, March 15, Mr. Allen put in half a 

 dozen ancyloids from the large jar. March 29 a mature 

 septate was taken out, and it was noticed that the Plan- 

 orbis looked frail as if insufficiently sup] died with lime 

 salts. October 11, 1909, two half-grown septates were 

 taken from this jar. In the winter (1909-10) the Plan- 

 orbis, for some unknown reason, completely disap- 

 peared. 



From these data Mr. Allen concludes that about 80 per 

 cent, of the stock in this jar had assumed the septate 

 form, the conditions obviously being such as to stunt 

 both Anacharis and ancyloids. In the 15 X 9-inch jar 

 the vegetation is luxuriant and abundant, and the sep- 

 tate individuals produced were only about two to five 

 per cent, of the ancyloids. From this Mr. Allen con- 

 cludes that the formation of a septum is promoted by 

 causes which tend to restrict or retard growth. 



The 9 x 7-inch Jar. — This has a mixture of sand and 

 soil at the bottom. There is plenty of algal growth, but 

 the Anacharis is not as vigorous as in the 15 X 9-jar, 

 from which it was stocked with ancyloids and Planorbis. 

 In the winter of 1900 07 it yielded two septates. The 

 winter of 1907 OS ancyloids were fairly numerous, more 

 so than during the first winter, but no septates were de- 

 tected. July 1, 1908, young fry, hatched that season, 

 were visible. March 8, 1908, a fine large mature Gund- 

 hichla was taken. The original ancyloid part was deep 

 black and the flaring expansion beyond it was colorless 

 and transparent. In the sand-bottomed jar the mature 

 Gundlachia is uniformly yellowish translucent, but in 

 the large jar with mud bottom the whole shell gets black- 

 ish. December 13, 1909, a census of this jar was at- 

 tempted. The day was dark and a count difficult, but the 

 result was six septates and two ancyloids, all eight being 

 small and immature. 



A Jar ivithout Planorbis.— Thinking it might be de- 

 sirable to have a stock of the ancyloids not associated 

 with Planorbis, Mr. Allen, about February, 1909, when 



