Nov. 5, 1874.J 



NA TURE 



After this extraordinary preface, Prof. Hrcckel enters on 

 the more serious part of the book by a history of the 

 doctrine of development. Passing rapidly from Aristotle 

 and the founders of biology in the sixteenth and seven- 

 teenth centuries, he describes at some length the dis- 

 coveries of Wolff (published in 1759), which were so long 

 and so unjustly neglected ; the scarcely less splendid 

 researches of the now venerable Von Baer (1827), and 

 those of Mr. Darwin, from the appearance of the " Origin 

 of Species" in 1859 to the present time. Among the 

 ontogenists, beside Wolff and Von Baer, whom he 

 justly places in the first rank, due mention is made 

 of Pander, Rathke, Bischofif, Johannes Miiller, KoUiker, 

 Remak, Fritz Miiller, and Kowalevsky. But while 

 most English cmbryologists (and histologists too) will 

 probably agree in substance with our author's judg- 

 ment on the doctrines of Reichert and of His, they 

 would scarcely speak of a distinguished living anatomist 

 as "dieserj auserordentlich unklare und wiiste Kopf." 

 Among the philogenists who preceded Darwin, particular 

 attention is paid to the speculations of Lamarck, in his 

 " Philosophic Zoologique," which were published in 1S09, 

 and thus exactly divided the century which elapsed be- 

 tween the first great work on the subject, Wolff's " Theoria 

 generationis," and the last, Darwin's " Origin of Species ; " 

 and also to those of Goethe, extracts from whose writings, 

 both prose and verse, are scattered up and down the 

 volume, not only in the text, but on the fly-leaves and 

 other blank spaces. We venture to think that both here 

 and elsewhere Prof. Hasckel has put too high a value on 

 these pre-Darwinian speculations. He discovers who 

 proves : and neither Lamarck nor Goethe could justify 

 their guesses by facts. They happened to be right, just 

 as among all the random guesses of the ancient Greek 

 cosmologists Thales happened to have hit on the true 

 relation of the sun to the earth, probably from his being 

 less and not more philosophical than his fellows. If 

 some of the assertions of modern spiritualists or phreno- 

 logists should hereafter turn out to be true, they would 

 no less destrve the condemnation of a future generation 

 for believing what, on the facts within their knowledge, 

 they had no business to believe. 



The chapters which succeed are devoted to a clear and 

 tolerably full account of the development of the human 

 embryo from the ovum-cell to the stratification of the 

 blastoderm. The only fault to find with this part of the 

 book (and its merits need no praise for those who are 

 acquainted with our author's skill in exposition of a diffi- 

 cult subject) is the exaggeration of such phrases as this : 

 " The process of fecundation is very simple, and involves 

 nothing at all peculiarly mysterious." In one sense, of 

 course, this is true ; the ultimate mystery of every func- 

 tion, organic or inorganic, is equal : but fecundation, like 

 other organic functions, has the peculiar mystery that we 

 cannot yet rank it with other mysteries. Most of us 

 believe that one day each movement of each particle of 

 the ovum will receive its appropriate physical explana- 

 tion, but till then we must be content to call them vital, 

 just as we call other movements chemical : and even a 

 popular lecture should not anticipate the advance of 

 science. 



The most important position maintained in this part of 

 the book is that in Vertebrata the two primitive blasto- 



dermic layers (epiblast and hypoblast of Huxley, exoderm 

 and entoderm) differentiate eac h into two, as in Vermes, 

 and that the mesoblast (motorgerminal layer of Remak) 

 subsequently arises by coalescence of Von Baer's Fleisch- 

 schicht or Hautfaserblatt and Gefiissschicht or Darm- 

 faserblatt. The various opinions which have been put 

 forth on this difficult subject are discussed, and the 

 author's view illustrated by some coloured figures. In 

 the number of the Quarterly Microscopical Journal for 

 last April there is an article by Prof. Hssckel (very ill- 

 translated) on the " Gastnca " theory which was put 

 forth in his valuable work on '■ Calcareous Sponges ;" 

 and there he discusses the homologies of the secondary 

 germ-layers. To it we may refer the English reader as 

 an exposition of this part of the subject, and unfortu- 

 nately as another instance in justification of what has 

 been said of the dogmatic confidence and undignified 

 personalities which disfigure the present volume. 



The description of the further development of the 

 human embryo, including a short account of the origin 

 of the various organs, is an excellent example of how a 

 very complicated subject may be explained and illustrated. 

 The figures from Bischoff, Kolliker, Gegenbaur, and other 

 anatomists are somewhat coarsely reproduced, but are 

 supplemented by some new drawings on stone. These 

 chapters, however, on human ontogeny and organogeny 

 are unexceptionable and somewhat commonplace. They 

 seem to be chiefly introduced for the sake of the philogeny 

 which occupies the third series of lectures. It is the 

 close connection between the known development of the 

 individual and the hypothetical development of the race 

 which it is the merit or demerit of the book to expound 

 to a popular audience, and to this subject we hope to refer 

 in a future article. 



LETTERS TO THE EDITOR 



[Tin Editor does not hold himself responsible for opinions expressed 

 liy his correspondents. Neither can he undertake to return, 

 or to correspond with the ivriters of rejected manuscripts. 

 No notice is taken of anonymous communications. ] 



Migration of Birds 

 I HAA'E to thank Mr. W.illace and Mr. Romanes for their 

 remarks (Nature, vol. x. pp. 459 and 520) on the article in 

 which I drew attention to this subject. The former especially 

 has laid all ornithologists under an obligation for the charac- 

 teristic skill with which he has iUustrated the way whereby 

 migratory habits have most likely been brought about. I think 

 it is veiy possible, as he suggests, " that every gradation still 

 exists in various parts of the world, from a comjilete coincidence 

 to a complete separation of the breeding and subsistence areas," 

 and that "we may find every link between species which never 

 leave a restricted area in which they breed and live the whole 

 year round, to those other cases in wiiicli the areas are absolutely 

 separated." Still, I cannot point out any species which I believe 

 to be, as a species, strictly non-migratory. No doubt many 

 persons would at first be inclined to name half a dozen or more 

 which are unquestionably resident with us during the whole year, 

 and even inhabit the same very limited spot. l)ut I think that 

 more careful observation of the birds which are about us, to say 

 nothing of an examination of the writings of foreign observers, 

 will show that none of them are entirely free from the migratory 

 impulse. Perhaps the nearest approach, among British birds, to 

 an absolutely non-migrant may be found in our familiar Hedge 

 Sparrow. Personally, I have never been able to detect any 

 movement in this bird, but one has only to turn to works on the 

 ornithology of the extreme north and south of Europe to see that 

 it is affected like the rest, and even in the Orkneys it is described 

 as an occasional autumnal visitant. However, in most of the 



