Amongst Birds, the most striking case is seen in the exceeding longevity, which is well ascertained, of Parrots. They are undoubtedly the very highest of Birds in development, and they live probably the longest. The facts as to age do not however relate to their normal potential longevity, we have to guess that from the experiment in abnormal conditions.

Next, as to generative expenditure.1 Since this generally and clearly increases with diminished evolution, it is not difficult to establish the contrast between it and high longevity, as a general rule. The Protozoa and Protophyta are exceedingly prolific, an Infusorian being calculated to produce 268 millions in the course of a single month (Paramecium) : another 170 billions in four days, and their duration of life is correspondingly of the shortest. Insects are exceedingly prolific, and hence, in spite of their high evolution, very short-lived. Many insects deposit 300,000 ova, but, what is a more important item of consideration, they deposit an enormous bulk relatively to their living matter. Compare the not far distant but inferior Annelids, and they are seen to be

1 It does not appear worth while to consider asexual and sexual genesis separately, where so little is to be said. But it does appear from the facts that asexual genesis is less severe a tax, and therefore less inimical to longevity than sexual genesis. Thus Chatogaster and other worms live and reproduce asexually in abundance, but at length sexual genesis occurs and they die. It is in those cases where asexual genesis partakes of the nature. of growth rather than germ-production that it is least severe in its effect on longevity.

longer lived, for though in most cases possessing large genital organs, they do not deposit their ova or sperm so early or so rapidly as the Insects. The Vertebrata are by no means prolific (except fish), and at the same time are longer-lived than Invertebrata.

Fish are long-lived, in spite of considerable generative expenditure,1 the explanation lying in the diminished personal expenditure involved in their aquatic life. This, too, affects greatly the case of Annelids just quoted. Amongst Birds it is easy to point out that smaller broods go with a greater longevity thus the Eagle has but one or two eggs, the common Owl four or five; Finches two broods of five in a season, and the Wrens and Tits eight to fifteen; and these, as appears from our list above, stand in the same order as to longevity. It is very difficult indeed to find particular cases in which the direct action of generative expenditure on longevity is apparent, for it affects other quantities before longevity, or its action is counteracted by fluctuations in these quantities, as,

1 The bulk of the ova and sperm in fish is not so large as the number of the ova lead one to think; and moreover, as a rule, they give no parental attention, which is a most important item of generative expenditure. In those fishes which do, e. g. Pipe-fish, Hippocampus, and Arius of the Amazons, the bulk and number of the ova is immensely reduced.

This item of parental attention is what in the case of man and other animals tends much to balance the male and female generative expenditure, for the male feeds both mother and young for a considerable time by his exertion; hence the female's expenditure of substance is in some degree balanced.

for example, in personal expenditure and degree of evolution. One ought to compare organisms which are alike in these two last quantities. In trees, we may take the pear, apple, and such fruit-trees, and we find that they are excessive in their reproductive expenditure, and short-lived as compared with other trees which agree (as do all Vegetals) in the absence of personal expenditure, and are of equivalent individuation. In animals1 we may best compare experimental cases: thus we find that animals used for breeding, and made to breed early, are less longlived than those which are not so used.2 There are, besides, two important cases to compare, viz. mules which are born incapable of reproducing, and animals which have been operated upon. With regard to the Mule, Bacon states that it lives longer than either the Horse or the Ass, which confirms the hypothesis that generative expenditure antagonizes longevity. But as to the results of operations, it appears that, as in cases of forced abstinence, a disturbing element is introduced by the interference with the proper functions and nutrition of the animal. The principle of Treviranus, 'that every organ is as an excreting gland to the rest of the body' must be remem

1 The case of Actinia is alluded to farther on. Its longevity is an example where small generative expenditure, either asexual or sexual, entails long duration of the individual.

2 This statement is derived from general assertions and needs confirmation.

bered, and we can comprehend that by the removal of generative glands no advantage as to longevity would accrue to the organism, but perhaps great injury, whilst the abeyance of normal functions will equally not prevent that nutrition of the organs and their growth, which is a great part of the tax of generative expenditure. At the same time, both castrated organisms, and those restrained from the sexual act, gain in the possible absence of nervous excitement, which has a relatively enormous costliness,' 1 and by not losing the simple weight of the emitted generative product. It does not appear from facts, that castrated animals are longer-lived than those normal, neither amongst men nor lower animals, nor that celibates, male or female, among either men 2 or lower animals, have a large if any advantage.

Passing on to personal expenditure, we find more numerous facts in the list to support our deductions. Aquatic animals, generally, have less personal expenditure than terrestrial animals; they are supported in the water, the temperature fluctuates little, their

2 It is exceedingly difficult to make estimation as to male celibates; the unmarried have a considerably higher death-rate at ages below fifty among males than the married, but there are not statistics to shew that of the numbers surviving there is a less expectation of life than among the married, or widowers. It is impossible to be assured of the strict abstinence of any group of men. Amongst women the oldest are widows, but the relative ages of marriage of males and females, and the numbers of married and unmarried affect these numbers vastly, and their influence cannot yet be eliminated.

food is abundant, for waters 'team with life' truly more than the atmosphere. Terrestrial animals, whilst supporting themselves mostly on the ground, live in the air, and in very few cases is their food to be found abundantly in this medium, and accordingly their expenditure in getting food is greater. Thus among Vertebrata, the Whale is long-lived, the Crocodiles and Chelonians are long-lived, the Salamandroids and the Fish. It does not appear certain that the Batrachia (Frogs and Toads) are shorter lived than the Salamandroids; their terrestrial habits involve greater expenditure, but their very much higher individuation may counterbalance this. Among Invertebrata, the Mollusca are long-lived; the Pulmonata less so than the branchiate Gasteropods. Paludina and Lymnæus living in the same pond differ thus in age, whilst no land Mollusc is as large (and therefore probably from what we have seen as long-lived) as many hundreds of aquatic (marine) species.

1

The aquatic Arthropods (Crustacea), excluding the minuter forms, are most broadly contrasted with the terrestrial Insects, Myriapods, and Arachnids, in respect of length of life, as we have before mentioned, and set forth in the list. Descending lower, we find no terrestrial groups to compare.2

1 As far as the writer's observations go, Lymnæus lives four years, and Paludina seven or eight.

2 There is the terrestrial leech, and there are the terrestrial Planariæ, or ground Flukes, the longevity of which is not ascertained.