4o6 



NATURE 



\_March 3, 1881 



Semper's contribution to the subject does not tend to 

 alter the low estimate which has been formed of the 

 efficiency of directly-transforming agents, nor to justify 

 the "final warning" which closes his book. It is then 

 as a repertory of physiological facts of a kind usually 

 neglected both by the professed physiologist and by the 

 professed zoologist that this book will be found of value, 

 not as the expository of new or of old theory. 



After an introduction in which, amongst others, some 

 interesting observations on the casting of the skin of 

 reptiles and of crayfish are given with illustrative cuts, 

 we find a chapter on " Food and its Influence." The 

 variety of mineral and organic substances which consti- 

 tute the food of animals is noted, and monophagous and 

 polyphagous animals distinguished ; curious adaptations 

 to a special food such as that of egg-eating snakes, with 

 their gastric teeth formed by processes of the vertebrae, 

 are cited, and some remarkable e.xamples of change of 

 diet naturally occurring in a species ■without any modiji- 

 cation of strticture, e.g. the New Zealand parrot, which 

 used to feed on the juices of plants and flowers, but now 

 sucks the blood of sheep. Again, horses eating pigeons, 

 vegetivorous snails (LymnJEus) eating young newts, croco- 

 diles, some eating men, and others of the same species 

 not prone to the habit. The only well-established in- 

 stances of modification of structure caused by change of 

 food are due to John Hunter, who fed a gull for a year on 

 grain, and so hardened the inner coat of the bird's 

 stomach as to make it resemble the gizzard of a pigeon ; 

 whilst Dr. Holmgren is cited as having obtained the 

 converse result by feeding a pigeon on meat. The change 

 brought about here is, however, not strictly speaking a 

 change of structure, but rather a modification of the 

 chemical activity of the gastric epithelium. 



Many instances of wide difference of diet in closely 

 allied species of animals not accompanied by any corre- 

 sponding difference of structure are given in the text and 

 in the valuable notes at the end of the book. 



The influence of light is next discussed, and we have 

 some statements as to the difference in their relation to 

 light, of plants and animals. Prof. Semper does not 

 admit the presence of chlorophyll in any animal, and goes 

 so far as to say that the similarity of the spectrum of the 

 solution of the green pigment of an animal with that of 

 chlorophyll would not prove the pigment to be chloro- 

 phyll. If by " similarity " exact correspondence is meant, 

 we should differ from him ; but it is no doubt true that 

 further exact observation is needed of those cases among 

 invertebrate animals in which chlorophyll has been 

 supposed to be present. 



Semper holds that there is a high degree of probability 

 in the view that the green-coloured bodies present in 

 some lower animals in such abundance are really parasitic 

 Algae like the gonidia of lichens. As an argument in 

 favour of this view he adduces Max Schultze's observa- 

 tion that the " chlorophyll-bodies '' of the wonn Vortex 

 ■viridis divide and multiply spontaneously, which he 

 states (in opposition to the generally received observa- 

 tions of Niigeh and the statements of his colleague Sachs) 

 the chlorophyll bodies of plants do not. It would be 

 interesting if this should prove to be the case, and if Prof. 

 Semper should be destined to reform our notions of 

 Vegetable histology among other things. 



In a note Semper attacks Paul Bert for saying that 

 " Infusoria containing green matter decompose carbonic 

 acid in the same way as vegetable cells." The French 

 physiologist is well within the facts, for Priestley's 

 green matter was the Flagellate Engleiia viridis. 



It is necessary to point out that it is by no means 

 proved by Cienkowski's observations that the yellow cells 

 of Radiolaria are parasitic one-celled Algae, as Semper 

 assumes, though it is possible that such is their nature. 



Light affects animals mostly through the eye only, and 

 its intensity undoubtedly has a modifying influence upon 

 that organ ; but whether the degeneration of the eye in 

 cave animals and deep-sea Fishes and Crustacea is due 

 directly to disuse in any instance or to altered selection 

 and heredity, is not clear. Many important facts and 

 some good drawings bearing on this matter are given. 

 Dr. Hagen informed the author that in all the species of 

 cave-beetles of the genus Machaerites the females only are 

 blind, while the males have well-developed eyes, although 

 both live together in total darkness, whilst it is well 

 known that many blind animals, e.g. certain Mollusks, 

 Crustacea, and Worms, live in bright daylight. 



Facts are cited showing that the colours of animals are 

 not developed by or dependent on light, whilst the 

 change of colour eff'ected by cuttle-fish, fishes, and Am- 

 phibia when light acts on the eye are discussed at length, 

 and the researches of Lister and of Pouchet cited. Prof. 

 Semper, in common with other naturalists, explains the 

 difficulty presented by the colouration of some animals, 

 such as those which live in the dark (many marine 

 polyps and worms), by the assumption that the pigment 

 is the inevitable secondary product of some indispensable 

 physiological process. The same explanation is applied 

 to the phosphorescent material of many marine organisms, 

 which is apparently useless or even injurious to the 

 animals which produce it. 



Temperature affords subject-matter for a chapter, 

 abounding in important records of fact, which are, it 

 must be admitted, quite antagonistic to the notion that 

 variations in the environment in this respect can directly 

 produce adaptative change of structure. The most re- 

 markable instance of temperature effecting a change of 

 structure is that quoted from Weissman, who, by arti- 

 ficially lov/ering the temperature, succeeded in rearing 

 Vanessa levana from the eggs of Vanessa prorsa-levana, 

 the two supposed " species," being only winter and 

 summer varieties of one. But here, though the colouring 

 is different in the two varieties, there is no adaptational 

 character about it, nor a transmission of the changed 

 colouring to offspring. 



A number of facts are cited as to the supposed change 

 of colour of Arctic animals in winter, but the conclusion 

 seems to be that no such change occurs. Facts esta- 

 blishing the possibility of freezing whole fish and other 

 animals are given, and otlier facts showing that 5° below 

 0° C. kills the tissues of such animals as frogs, and may 

 thus cause death to the whole animal. Important re- 

 seai'ches of Horvath are cited, showing that the Ground- 

 squirrel (Spermophilus), the temperature of whose body 

 is in summer like that of man, about 38^ C, can, during 

 its winter sleep, sink to as low a temperature as 2° C. 

 without injury ; its body, in fact has, at this period, the 

 same temperature as that of the surrounding air. The 



