May io, 1894] 



NATURE 



31 



I need not multiply examples of this world-wide fallacy. We 

 have the two words viass and weight ; let us keep them distinct, 

 and thereby help towards an understanding of the nature of an 

 absolute unit of force and other physical entities. 



"K."says " the earth's weight, or mass, is 6' 14 >: lo'-' tons. 

 What is unmeaning; or unscientific in this clear, intelligible, and 

 accurate statement ? " Answer, the identification of meight with 

 mois. He is mistaken in supposing that Prof. Poynting's book 

 has a double title. It is simply "The Mean Density of the 

 Earth." The determination of the ''constant of gravitation" 

 is a deduction, and is, of course, so treated by Prof. Poynling. 



The Reviewer. 



Icebergs and Weather. 



With reference to the notice in Nature of May 3 (page 15), 

 of a letter by Mr. Russell on icebergs and their relation to 



weather and temperature, I should like to give you a personal 

 experience of my own with an iceberg in mid-Atlantic, when on 

 board the steamship India, on its voyage from New York to 



Newcastle. on-Tyne, in June last year. 



Our recorded temperatures of 43" F. and 45° F. of one day fell 

 to 34° F. in water and in air on the next day. On reporting 

 this to the chief officer, an extra look-out was kept, and the 

 vessel put on half speed, as the weather was foggy, and icebergs 

 were likely to account for the sudden fall of temperature. 

 Twenty minutes afterwards an iceberg was sighted, which 

 showed a length of 1200 feet, and a height of 200 feet above 

 water. 

 Leeds, May 7. A. Sydney D. Atkinson. 



Early Arrival of Birds. 



I WAS at Sellack, Ross, Herefordshire, on March 22 and 

 following days. Chitf-chaffs had arrived on the 22nd ; cuckoos 

 were heard on the following day. The willow-warbler 

 and garden-warbler followed. 



In quest of food, birds follow the path of least resistance. 

 Thus their migrations, in the economy of nature, depend not 

 simply on food, power of flight, distances, temperatures, &c., 

 but on the associated extent of systems of wind. 



May 4. W. Clement Lev. 



THE EFFECT OF EXTERNAL CONDITIONS 

 UPON DE VEL 0PM EN T. ' 



'X'HERE is now ample justification for the belief that 

 ■«• evolution is not due merely to internal causes, 

 though we are as yet by no means quite clear as to the 

 manner in which external influences have formed and 

 transformed organisms. There is still a conflict between 

 rival theories, and important points, though often ap- 

 parently clear, are in reality not so. 



It is often assumed, without sufficient proof, that a 

 particular variation of an organism is the direct con- 

 sequence of some external influence, simply because 

 some causal connection exists between the two ; but 

 «uch an assumption is based upon a totally false idea as 

 to the interconnection of the phenomena. In many cases 

 this will be readily granted ; take, for instance, that of the 

 leaves of A/imdsci, which close when they are touched. The 

 actual cause of the movement is here due to the peculiar 

 constitution of the plant, and not to the touch. 

 The geotropism of plants, again, is not the direct effect 

 of gravity, but is due to a special power of adaptation 

 possessed by the plant. In reference to the histological 

 adaptation of animal tissues, let us take as an example 

 the structure of the lattice-work in spongy bones. Roux 

 has shown that this is due to processes of selection and 

 for a struggle for existence between the various parts of 



* Abstract of the Romanes Lecture delivered in the Sheldoni.la Theatre 

 at Olford, on May s, by Prof, .\ugust Weismann, Ph.D., D.C.I.. 



the body. Prof. Weismann speaks of this process as 

 " intra-selection," and attempts to show that its effects 

 are not inherited, as assumed by Roux, but that heredity 

 only concerns those potentialities from which structures 

 are developed by intra-selection. He believes that the 

 potentialities have not arisen through the struggle be- 

 tween the parts of an organism, but through that between 

 individuals : not by intra-selection, but by the ordinary 

 process of natural selection. The causa efficicns of this 

 histological adaptation is not. therefore, the tension or 

 pressure which acts on the bones, but the adaptive 

 material upon which such forces operate. The theory of 

 intra-selection thereby loses nothing of its value, but on 

 the contrary, is admitted to be of the greatest importance 

 in maintaining the "co-adaptation" of parts during the 

 metamorphosis of species. 



The organism can, however, also be affected by ex- 

 ternal influences for which it is not adapted in advance. 

 This is the case as regards the ordinary seasonal dimor- 

 phism of butterflies ; but even seasonal differences may 

 be produced by adaptation — here a double adaptation — 

 in which the external influences of temperature do not act 

 as the direct causes of change, but only as stimuli, 

 which detennine as to which of the two forms of the 

 species shall arise. 



In the case of neuters of social insects, the external 

 influence — scanty food — is not, as Herbert Spencer as- 

 sumes, the true causa efficicns which produces the 

 sterility of their caste, but only the stimulus by which 

 the primary constituents {Anlai^c7i) of the worker-type are 

 brought into activity. At least three kinds of primary 

 constituents — those of the male, the fertile female, and 

 the worker — must be contained in the eggs of ants, bees, 

 and termites ; the nature of the stimulus acting upon the 

 egg determines the kind of primary constituent which 

 shall come into activity. These opinions are confirmed 

 by experiments made on flies, which show that in- 

 sufficient nourishment supplied to the larva does not in 

 any way affect the development of the ovary. The 

 disappearance of typical organs — such as the ovarian 

 egg-tubes of bees and ants — is thus shown to be a 

 phylogenetic and not an ontogenetic process : it does not 

 depend on mere influences of nutrition, but on variation 

 in the primary constituents of the germ ; and thus can 

 only come about in the course of numerous generations. 

 The case of social insects is therefore far from con- 

 tributing any support to the view that acquired characters 

 are inherited, and that the inheritance of the effects of 

 use or disuse play a part in the transformation of species, 

 as is assumed by Herbert Spencer. 



Thus we see that external influences in many cases 

 serve as the impulse which starts the process of develop- 

 ment in certain of the primary constituents. The actual 

 cause of these individual dissimilarities is in all cases to 

 be sought in the modification occurring amongst the 

 primary constituents of the body itself; and such pur- 

 poseful modifications can only have originated by 

 selection. Even when to all appearance external in- 

 fluences have had direct action in causing purposeful 

 modifications, a more careful examination will always 

 show that they have only served to bring some preformed 

 adaptation into activity. This is proved in a specially 

 conclusive manner by the consideration of sterility in the 

 workers of bees and ants : the sterility is not due to 

 poor nourishment, but to natural selection, which has 

 determined the nature of the primary constituents in the 

 ovary. This case is of especial interest, as it has been so 

 much relied on as a support to the Lamarckian principle 

 of the inheritance of acquired qualities. Here, as in all 

 other instances, the Lamarckian hypothesis is untenable ; 

 selection has been the only principle on which the 

 development of the organic world has been guided on 

 its course. 



NO. 1280, VOL. 50] 



