REVIEWS. 



EVOLUTION'. 



Convergence in Evolution. — By Dr. Arthur Wili.ev, 

 D.Sc, F.R.S. 177 pages. 12 illustnitions. 8f -in. X 5A-in. 



ijohn MuriMv. Price 7 6 net. I 



Dr. Willey writes, he says, so as to be intelligible to those 

 who have an inkling of biological knowledge, bnt it is 

 probable that his argument as a whole will hardly be 

 appreciated save by trained zoologists. Nevertheless, there 

 is an abundance of facts recorded, many of them new and all 

 interesting, that should appeal to every naturalist however 

 much of an amateur he may be : and it is safe to say that 

 even a professional zoologist will learn much to his advantage. 

 The author sets out by reviewing certain points in the grouth 

 of the science of morphology and its kindred brunches which 

 have rendered them valuable both as intellectual recreations 

 and as of direct practical use to mankind. He goes on to 

 suggest ihat we may look to other properties of animals 

 besides those of structure to gain a comprehensive survey of 

 the animal kingdom. Without going so far as to compare the 

 value ot classification based on structure with that based on 

 similarity of function, he asserts that too little attention has 

 been paid to what may be called physiological systems of 

 classification. .\ir breathers, and water breathers, fixed 

 forms (statozoa) and free forms (eleutherozoa), light avoiding 

 habits (cryptotaxisl. and light seeking habits (phanerotaxis), 

 and so on. are compared together, with a host of interesting 

 and illustrative facts of natural history, many of them 

 personally observed by the author. Similar habits and 

 environment have brought about similar structure : in other 

 words, convergence and parallelism have been far more potent 

 factors in evolution than is generally believed, and the same 

 structure in homogenous animals has nevertheless often 

 been independently acquired. Especially applicable are 

 his ideas of convergence, divergence and parallelism to 

 the parallel series of marsupials and placentals : perhaps 

 the most convincing arguuient in the book. According 

 to Dr. Willey, convergence may be traced in the anatomy, 

 bionomy, physiology and histology of animals closely 

 related and widely dissimilar, e.g., the pectoral fins of 

 flying fishes, and the solenocytes of .\mphioxus and the 

 Polychaetes, to take but two examples. He might also have 

 added psychology as well. Nothing is clearer from the results 

 of anthropological research, than that the dift'crent races of 

 men. separated by the whole length of the globe, have evolved 

 •almost, if not quite, the same myths and folk-lore, indepen- 

 dently of one another. 



Nevertheless it must be confessed that the ordinary zoologist 

 will not feel that his cherished beliefs and traditions have been 

 seriously undermined by Dr. Willey"s book. The true test of 

 relationship of animals must be based on the structure of 

 modern and extinct forms, and this fact Dr. Willey would 

 himself probably be nuwilliug to challenge; and although such 

 eminent writers as Dr. Gaskell, whose theories as to vertebrate 

 origin the author extensively quotes to refute, may be led into 

 situations where the finding of homologies based on structural 

 resemblance takes on an almost terrifying aspect, yet the 

 main principle holds good. 



Here and there, e.g.. on page 10, it is not easy (juite to 

 understand what is meant, but. as a whole, the book is clearly 

 and brightly written. \r n H 



Neglected Factors in Evolution. — Hy H. M. Bernard. 

 489 pages. 47 illustrations. Sj-in. X 5n-in. 



(G. Putnam's Sons. Price 12, 6 net.) 



It not infretjuently happens, and this book is a case in 

 point, that a biologist after years of work in some more or 

 less restricted branch of his subject, it hardly matters what, 

 proceeds to the most far-reaching generalisations. We are 



far from deploring this tendency, though at times it is 

 accompanied by a want of sense of proportion, patent to all 

 save the author himself. For it is an undoubted fact that 

 careful observations even of a limited scope, coupled with 

 sound reasoning and a sufficient dose of imagination, have in 

 the past, as they will in the future, ^ • ■■^•onized biological 

 science. We leave our readers t^ i a- themselves if 



this is true of Mr. Bernard's work. i .i author is chiefly 

 known for his researches on the histology of the retina, and on 

 the morphology of the apodidae and of other arthropods. 



The book is divided into two parts. The first, however 

 much we may disagree with the conclusions therein arrived 

 at, is a valuable contribution to cytology. It is clearly 

 written throughout, and Mr. Bernard never forgets the point 

 of view which most biologists hold on the Cell Theory. That 

 the facts observed necessarily prove the theory does not 

 follow, though there is much to be said in support of it. 

 yet the author's careful summary of the facts in itself 

 is a valuable piece of work. .\ long study of the minute 

 structure of the human retina convinced him that the 

 views commonly held as to the fundamental nature of 

 tissues in general are untenable. In common with Whitman, 

 Sedgwick, and others, he refuses to look on cells as the lowest 

 units of life. The structure of bacteria and of some protozoa, 

 and the histology of the metazoa prove, he thinks, that 

 organisms are not made up of cells but of smaller units, which 

 he calls chromidia. A cell is simply a complicated tangle of 

 chromidia. and cell-boundaries are always indefinite and of 

 little importance. In fact protoplasm is made up of a 

 network of living threads, visible only when they are coated 

 with some stain-receiving matter, on which are threaded 

 lumps of chromatin. This latter substance he believes to be 

 chiefly made of complex chemical bodies necessary for 

 the life of the filaments. A simple chromidium consists of a 

 small lump of chrouratin provided with a number of radiating 

 threads along which it can creep backwards and forwards, 

 bathed in a nutritive albuminous matrix. He points out that 

 such a view of cell structure brings into harmony the well- 

 known views of Butschli and Altmann as to the structure of 

 protoplasm ; with great ingenuity he applies this conception to 

 explain not only the structure of a typical cell, but qf cilia, 

 flagella, ecto- and endo-plastic skeletons, and even the 

 phenomena of mitosis. Though in justice to the author 

 it should be remarked that few difficulties are shelved, yet 

 more attention should have been paid to the discoveries of the 

 "' EIntwickelungsmechaniker.'' The fact that isolated blasto- 

 meres of developing eggs can produce a perfect though much 

 reduced larvae hardly squares with his theory. Mr. Bernard 

 believes that the cell theory in its present shape stands in the 

 path of further progress in cytology, while his theory of a 

 primitive network, protomitome. pervading the whole organism, 

 certainly does away with some of the difficulties attending a 

 comprehensive understanding of tissue formation. Further- 

 more, we are shewn the way in which the metazoa might have 

 been evolved from an unicellular ancestor. .'\11 this is very 

 interesting, and, if not convincing, is at all events well worth 

 reading. 



Part 2 contains far more theory and less fact. Postulating 

 a kind of rhythm -in evolution, the author sug.gests that the 

 factors according to Darwin are insufficient to explain the 

 gradual development of a highly dift'erentiated organism such 

 as Man. He believes that evolution has been marked by 

 periods at the end of each of which an outburst of activity 

 has taken place resulting in colony formation. A colony 

 of chromidial units becomes a cell, a colony of cell units 

 becomes a gastrael unit, a colony of gastrael units 

 forms an annelidan unit. Some such creature as an annelid 

 gave rise in the process of evolution to vertebrates, culminat- 

 ing in Man himself. The fifth evolutionary colony formation 

 has Man as its unit, the colony itself being human societies. 

 Just as the physical bodies of all the five units consist of a 



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