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NATURE 



{March 6, 1890 



has been carried out on the same elaborate scale. After 

 the British Empire, special prominence has been given 

 to the United States, whilst all the other countries of 

 the world have been treated in a very comprehensive 

 manner. The general reference index comprises the 

 names of 100,000 places contained in the maps, and for 

 British names it is the most complete ever published. 

 One matter of regret, however, is that the places on some 

 of the maps are not obviously visible because of the 

 bright and superabundant colouring used to indicate the 

 divisions of a country, for, generally speaking, these 

 divisions are better represented by coloured lines. The 

 less masking there is, the more distinct must places 

 appear, and therefore the purpose of an atlas will be the 

 better served. This is, however, but a minor point. The 

 atlas is an excellent one, it is complete and accurate, 

 contains all the results of recent exploration and geo- 

 graphical research, and is issued at a moderate price ; its 

 addition to every library therefore is a thing to be desired. 



The Bala Volcanic Series of Caernarvonshire and As- 

 sociated Rocks J being the Sedgwick Prize Essay for 

 1888. By Alfred Harker, M.A., F.G.S., Fellow of St. 

 John's College, and Demonstrator in Geology (Petro- 

 logy) in the University of Cambridge. (Cambridge : 

 University Press, 1889.) 



In this useful little work, Mr. Harker has given an 

 admirable resume of the results which have, up to the 

 present time, been arrived at by the study of the ancient 

 igneous rocks of North Wales. Besides summarizing the 

 work of the late John Arthur Phillips and E. B. Tawney, 

 of Prof, Bonney, Mr. Rutley, Mr. Cole, Mr. Teall, Mr. 

 Waller, Miss Raisin, and others who have written on the 

 petrography of the district, he has added many new and 

 often judicious notes on the rocks in question. A number 

 of fresh analyses, and the description of hitherto unrecog- 

 nized varieties of rocks and minerals, raise the work 

 out of the category of mere compilations ; and the excel- 

 lent classification and arrangement of his materials make 

 the book one eminently useful for purposes of reference. 

 It is unfortunate that it has no index, though the '' table 

 of contents," which is very full and carefully paged, 

 causes the want to be less felt than it otherwise would 

 be. Mr. Harker classifies the districts of Caernarvon- 

 shire in which volcanic rocks are found as the Eastern, 

 North- Western, and Western, the latter consisting of the 

 Lleyn peninsula. He groups the types of rocks repre- 

 sented under the headings of " rhyolitic lavas," " nodu- 

 lar rhyolites," "acid intrusives," "intermediate rocks," 

 " diabase sills and basalts," and "other basic intrusions." 

 The work concludes with a " review of vulcanicity in 

 Caernarvonshire," in which we find discussions of the 

 relation of the volcanic eruptions to the earth-movements 

 that took place at the period of their occurrence, the suc- 

 cession of lavas in the district, and the evidence in favour 

 of their submarine origin. The book is admirably 

 printed, and is illustrated by six very clearly-dra.wn 

 sketch-maps. The essay is worthy of the memorial in 

 connection with which it appears, and is creditable to the 

 University under whose auspices it is issued ; and higher 

 praise than this it would be difficult to give to any work 

 of the kind. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other fart of Nature, 

 No notice is taken of anonymous communications. "X 



The Inheritance of Acquired Characters. 

 Without expressing any opinion upon the question recently 

 discussed in your columns under the above title, I think it may 



be as well to recall the belief of one whose judgment was not 

 without weight, and to give some of the evidence on which that 

 belief was founded. 



In the first chapter of the " Origin of Species" (p. 8 of the 

 sixth edition), Mr. Darwin says, respecting the inherited effects 

 of habit, that "with animals the increased use or disuse of parts 

 has had a more marked influence " ; and he gives as instances the 

 changed relative weights of the wing-bones and leg-bones of the 

 wild duck and the domestic duck, and, again, the drooping ears 

 of various domestic animals. Here are other passages taken 

 from subsequent parts of the work : — 



" I think there can be no doubt that use in our domestic 

 animals has strengthened and enlarged certain parts, and disuse 

 diminished them ; and that such modifications are inherited " 

 (p. 108). And on the following pages he gives five further 

 examples of such effects. " Habit in producing constitutional 

 peculiarities, and use in strengthening and disuse in weakening 

 and diminishing organs, appear in many cases to have been 

 potent in their effects " (p 131). "When discussing special 

 cases, Mr. Mivart passes over the effects of the increased use 

 and disuse of parts, which I have always maintained to be highly 

 important, and have treated in my ' Variation under Domestica- 

 tion ' at greater length than, as I believe, any other writer " 

 (p. 176). "Disuse, on the other hand, will account for the less 

 developed condition of the whole inferior half of the body, in- 

 cluding the lateral fins " (p. 188). " I may give another instance 

 of a structure which apparently owes its origin exclusively to use 

 or habit" (p. 188). " It appears probable that disuse has been 

 the main agent in rendering organs rudimentary " (pp. 400-401). 

 " ( >n the whole, we may conclude that habit, or use and disuse, 

 have, in some cases, played a considerable part in the modifica- 

 tion of the constitution and structure ; but that the effects have 

 often been largely combined with, and sometimes overmastered 

 by, the natural selection of innate variations" (p. 114). 



In his subsequent work. "The Variation of Animals and 

 Plants under Domestication," he writes : — 



" The want of exercise has apparently modified the propor- 

 tional length of the limbs in comparison with the body " [in 

 rabbits] (p 116). " We thus see that the most important and 

 complicated organ [the brain] in the whole organization i- 

 subject to the law of decrease in size from disuse " (p. 129). He 

 remarks that in birds of the oceanic islands "not persecuted by 

 any enemies, the reduction of their wings has probably been 

 caused by gradual disuse." After comparing one of these, the 

 water-hen of Tristan D'Acunha, with the European water-hen, 

 and showing that all the bones concerned in flight are smaller, 

 he adds : — " Hence in the skeleton of this natural species nearly 

 the same changes have occurred, only carried a little further, as 

 with our domestic ducks, and in this latter case I presume no 

 one will dispute that they have resulted from the lessened use of 

 the wings and the increased use of the legs " (pp. 286-87). " As- 

 with other long-domesticated animals, the instincts of the silk- 

 moth have suffered. The caterpillars, when placed on a mulberry 

 tree, often commit the strange mistake of devouring the base of 

 the leaf on which they are feeding, and consequently fall down ;. 

 but they are capable, according to M. Robinet, of again crawling 

 up the trunk. Even this capacity sometimes fails, for M. Martins- 

 placed some caterpillars on a tree, and those which fell were not 

 able to remount and perished of hunger ; they were even in- 

 capable of passing from leaf to leaf" (p. 304). 



Here are some instances of like meaning from vol. ii. : — 



' ' In many cases there is reason to believe that the lessened use 

 of various organs has affected the corresponding parts in the oil- 

 spring. But there is no good evidence that this ever follows in 

 the course of a single generation. . . . Our domestic fowls, 

 ducks, and geese have almost lost, not only in the individual but 

 in the race, their power of flight ; for we do not see a chicken, 

 when frightened, take flight like a young pheasant. . . . With 

 domestic pigeons, the length of sternum, the prominence of its 

 crest, the length of the scapulas and furcula, the length of the 

 wings as measured from tip to tip of the radius, are all reduced 

 relatively to the same parts in the wild pigeon." After detailing 

 kindred diminutions in fowls anri ducks, Mr. Darwin adds, 

 "The decreased weight and size of the bones, in the foregoing, 

 cases, is probably the indirect result of the reaction of the 

 weakened muscles on the bones" (pp. 297-98). "Nathusius has 

 shown that, with the improved races of the pig, the shortened 

 legs and snout, the form of the articdar condyles of the occiput, 

 and the position of the jaws with the upper canine teeth project- 

 ing in a most anomalous manner in front of the lower canines, 

 may be attributed to these parts not having been fully exercised. 



