Illustrations 



1 7 (a) Growth-constant for growth in length of the sturgeon, 

 Acipenser stellatus, at various ages 72 



(b) Growth in weight of the sturgeon (Acipenser stellatus) 



and the bream (Abramis brama) 73 



(c) Growth in weight of the Bream (Abramis brama) 74 



1 8 (a) Life-table of Lebistes reticulatus 75 

 (b) Growth of female Lebistes reticulatus 76 



19 Growth of Emys 78 



20 Survival curves for Lecane inermis 86 



21 Growth in length of Philodina citrina 87 



22 Life-span and egglaying of Philodina citrina over 6 genera- 

 tions in normal culture 88 



23 Progressive decline in life-span of a strain of Philodina 

 citrina (Rotifera) raised in each generation from eggs laid 



by old mothers 89 



24 Life-span of successive generations of Philodina reared in 

 each generation from the eggs of 4, 11, and 1 7 day old 

 mothers 90 



25 (a) Growth of Daphnia magna — first type 93 



(b) Growth of D. magna — second type 94 



(c) Growth of D. magna — third type 95 



26 Survival curves of 143 isolated virgin females and 44 

 isolated, fertilized females of the moth Fumea crassiorella 99 



27 Egg production of Eulota fruticum 103 



28 Life-span of the pulmonate Limnaea columella 105 



29 Growth and longevity of Patella vulgata in various stations, 

 showing the short life of rapidly-growing populations 106 



30 Smoothed survival curve for the vole, Microtus agrestis in 

 captivity 109 



31 Survival curves of mice in laboratory culture — breeding 

 females 122 



32 Drosophila subobscura. Strain K. Survival curves of flies 

 raised in each generation from eggs laid by adults which 



had passed the 30th day of imaginal life 1 24 



33 Drosophila subobscura — hybrid vigour and longevity. Sur- 

 vival curves for the inbred lines B and K, and for the 

 reciprocal hybrids between them 128 



34 Survivorship curves for 82 males and 45 females of the 

 black widow spider Latrodectes mactans 131 



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