Published online by Cambridge University Press: 15 September 2014
Numerous authors have been concerned with phenomena and problems of senescence, duration of life, order of dying-out, and related subjects. With the exception of studies on Drosophila (Pearl and Parker, 1921; Pearl, 1922), other insects (for literature see Korschelt, 1924) and, in some respects, human subjects (see actuarial literature), most of the research of previous authors was embarrassed by the lack of sufficiently large and sufficiently homogeneous material; many conclusions rest on an insecure basis, since they refer only to isolated specimens or to experiments carried out on small numbers of animals.