According to Brehm the foot of these cliffs is ‘always covered with blood and the dead bodies of fledglings.’ Such birds must attain a great age or they would have been exterminated long ago: the minimum duration of life necessary for the maintenance of the species must in their case be a very high one. Note 2. The Duration of Life among Mammals. The statements upon this subject in the text are taken from many sources; from Giebel’s ‘Säugethiere,’ from Oken’s ‘Naturgeschichte,’ from Brehm’s ‘Illustrirtem Thierleben,’ and from an essay of Knauer in the ‘Naturhistoriker,’ Vienna, 1880. Note 3. The Duration of Life among Mature Insects. A short statement of the best established facts which I have been able to find is given below. I have omitted the lengthening of imaginal life which is due to hybernation in certain species. In almost all orders of insects there are certain species which emerge from the pupa in the autumn, but which first reproduce in the following spring. The time spent in the torpid condition during winter cannot of course be reckoned with the active life of the species, for its vital activity is either entirely suspended for a time by freezing (_Anabiosis_: Preyer[8]), or it is at any rate never more than a _vita minima_, with a reduction of assimilation to its lowest point. The following account does not make any claim to contain all or even most of the facts scattered through the enormous mass of entomological literature, and much less all that is privately known by individual entomologists. It must therefore be looked upon as merely a first attempt, a nucleus, around which the principal facts can be gradually collected. It is unnecessary to give any special information as to the duration of larval life, for numerous and exact observations upon this part of the subject are contained in all entomological works. I. Orthoptera. Gryllotalpa. The eggs are laid in June or July, and the young are hatched in from two to three weeks; they live through the winter, and become sexually mature in the following May or June. ‘When the female has deposited her eggs, her body collapses, and afterwards she does not survive much longer than a month.’ ‘According as the females are younger or older, they live a longer or shorter life, and hence some females are even found in the autumn’ (Rösel, ‘Insektenbelustigungen,’ Bd. II. p. 92). Rösel believes that the female watches the eggs until they are hatched, and this explains the fact that she outlives the process of oviposition by about a month. It is not stated whether the males die at an earlier period.