168 ANNALS OF SCOTTISH NATURAL HISTORY 



prolific some of these creatures are, the following statements 

 are submitted : A few months ago, when examining some 

 Catherines of freshwater entomostraca, I selected at random 



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ten specimens of Daphnia pulc.v and counted the number of 

 ova and embryos in each : in some of the specimens the ova 

 were in the earlier stages of development, in others the 

 embryos were well formed. The first specimen examined 

 contained 27 ova ; in the second there were 30 ; in the 

 third, 32 ; in the fourth, 20 ; in the fifth, 23 ; in the sixth, 

 32 ; in the seventh, 18 ; in the eighth, 18 ; in the ninth, 16 ; 

 and in the tenth, 20 in all 236 ova and embryos, or an 

 average of 23.6 for each Daphnia. Many years ago the late 

 Dr. Baird, the eminent English naturalist, made a number of 

 experiments with DapJmia pulex, and the following brief 

 statement of some of the results he obtained throws much 

 light on the fecundity of the species. 1 I give the results of 

 the experiments in his own words : " 29th November, I 

 isolated a D. pnJex with an ephippium ; 3Oth, ephippium 

 is thrown off; 4th December, Daphnia has eggs ; 8th, young 

 ones are born ; pth, the mother, having been removed from 

 the young immediately after their birth, was found to have 

 eggs again ; i6th, young ones born ; 2oth, has eggs again ; 

 24th, young ones born ; 25th, has eggs again ; 6th January, 

 young born mother has eggs in ovary again ; 1 4th, young 

 born mother has eggs again; 22nd, young born; ist 

 February, has eggs again ; 8th, young born. 



" On the 8th December, isolated one of the young born 

 from the subject of last series of observations on 3Oth 

 November. On the 2 i st December she was found to have 

 eggs ; 28th, young born ; 29th, has eggs again ; 9th January, 

 young born mother has eggs again ; 24th, young born ; 

 25th, has eggs again ; ist February, young born mother 

 has eggs again ; 9th, young born ; 27th, has eggs again ; 

 8th March, young born " (" Natural History of the British 

 Entomostraca," p. 80, 1850). Dr. Baird also states that he 

 isolated two specimens born on i 8th January, and that both 



1 Although Dr. Baird's experiments are made use of here to prove the fertility 

 of Daphnia, the purpose he had in view was rather to show that though the 

 Daphnia.' are not hermaphrodite, as had been supposed, one union with the male 

 "is sufficient not only to fecundate the mother for her life, but all her female 

 descendants for several successive generations." 



