AN ESS A Y ON LONGEVITY. 55 



Statements as to Duration of the Individual in 

 Organisms. 



ANIMALS. 



PROTOZOA. — Cause of death is the breaking up of this whole living 

 substance into generative particles, or its division into two 

 or more new individualities. Persistence of life unknown in 

 nearly all cases. 



Protomyxa aurantiaca — a Moneron — is stated by Haeckel to take 

 from 4 to 6 days in the process of division. (Monogr. of 

 Monera. Quarterly Journal of Microsc. Science, 1869.) 



Ammha probably takes longer. 



Infusoria have been seen to divide every half hour. (H. Spencer.) 



Zoolhamnium — a Vorticellidon — every 2 hours. (Brightwell.) 



* Sfongilla fluviatiUs dies yearly, leaving reproductive masses, the 



so-called seeds. 

 CCELENTERATA (Polyps). — Some appear to die annually or on repro- 

 duction, others continue to live and grow till mechanical 

 causes bring death. 



* Hydra viridis reproduces sexually in the autumn and dies. 



* Actinia mesembryanthemum has been living 42 years in an aquarium. 



(Sir John Dalyell and Dr. Flemming.) ^ 



Compound Hydrozoa live for a much longer period than one year. 



Compound Aclinozoa also ; but the masses of coral in the Red Sea, 

 estimated by Ehrenberg to be 3000 years old, do not indicate 

 the longevity of simply a tertiarily aggregated individual, but 

 of many generations of asexually produced individuals whose 

 parent stocks have died time after time. 



ECHINODERMATA, from the great variation in size of mature speci- 

 mens of the same species, are inferred to die only from me- 

 chanical or accidental causes. No observations on record. 



1 A letter from Mr. C. W. Peach informs me that ' granny,' as this 

 Actinia is called, is still alive and well, in spite of once being accidentally 

 buried in white-wash. 



