CHANGKS IN' KNV[RONMENT OP DAPHNIA MAGNA. 



217 



shorter by several liiindredths of its body-length than if it 

 had lived in an unlimited bulk. 



2. The influence of a confined volume of water 

 on the rate of growth and reproduction. 



(a) The History of the "A," ''a," and ''&" Families. 

 The differences in the conditions of life in the three series 

 of tumblers used in the previous experiment produced a con- 

 siderable effect on the rate of reproduction ; a small supply 

 of water decreased in a marked manner the number of 

 generations and the number of offspring in a brood. The 

 following table gives the mean dates at which broods were 

 produced, and the total number of offspring in each series. 



Table VI. 



Series " A " 

 (no fresh water iidiled). 



Series "a " 

 (a little rain water added). 



Series " b" 

 (water constantly clianged). 



The four mothers put in i 

 tumblers and product d ' 

 broods of the — 

 1st generation, "] 



July 23rd (20i) I „ , 

 2nd generation, [ 



Aug. 7th (17). J 

 3rd generation, 



Aug. 30th (12) 23.iaysi 



1st generation, 

 .July 23rd (14) 



2nd generation, 

 Aug. 8th (13).. 



3f.l generation, 

 Aug. 29th (15) 



"16 days 



21 days 



These individuals of the 3rd generation grew ex- 

 ceedingly slowly. About twelve young were pro- 

 duced towards the end of September and then 

 breeding stopped, and all the individuals were dead 

 by the beginning of December. 



1st generation, 



July 23rd (15) 

 2iid generation, 



Aug.7th(25-10), 

 3rd generation, 



Aug. 25th (23) 

 ith generation, 



Sept. 8th (22) . 

 5th generation, 

 Sep. 23rd (25-14) 

 6th generation, 



Oct.9th(24-12) 

 7th generation, 



Nov. 4th (16) . 



■15 da 



Although the water was 



continually changed t«o 



of the families died out, 



Fresh Daphuia from the tank were put into these ' and the others were in a 



tumblers on December 10th. They very soon be- ' sickly condition on Dec 



[ime unhealthy in appearance, and some died in 15th. 

 about a fortnight. Very few young were produced, 

 ;tnd all the animals were dead early in January. 



The temperature was kept at about 17° C. 



Fresh Daphnia taktii 

 from the tank and put into 

 the same tumblers, with 

 the same mud, lived and 

 produced broods in a per- 

 fectly normal manner. 



^ These are the number of young produced by the four mothers. 



