Nov. 12, 1874J 



NATURE 



23 



gradation of living animal forms, takes as the most im- 

 portant clue in his difficult task the facts of human 

 embryology. This close connection is constantly kept in 

 view, and by its aid not only does he trace, as in the 

 twenty-second chapter of his " Schopfungsgeschichte," 

 the philogeny of man as a compound organism ( Person), 

 but extends the same process to the separate organs of 

 the human body and the faculties of the human mind. 

 The chapters which are occupied by this investigation 

 are the most interesting in the book, full of ingenious sug- 

 gestions, and well repaying the reader who brings a sound 

 knowledge of embryology and comparative anatomy to 

 their study. 



The genealogical tree here constructed is briefly as 

 follows : — First, a Cythode {Moiicr), itself the product of 

 inorganic matter, passed in the Laurentian ages from 

 being a component of primordial sea-slime {Plasson, 

 represented by existing Bathybius) to a separate unicel- 

 lular or ama;boid form. Several of these plastids next 

 formed a colony by cell-division {Morula), which in sub- 

 sequent ages became covered with cilia, differentiated 

 into an ectoderm and entoderm, and provided with a 

 mouth {Casiraa), a form represented in sponges and other 

 invertebrates and in Amphioxys, but omitted in the onto, 

 genesis of man, or represented by the Blastosphere. 

 Each of the primitive layers subdivided into two, and 

 between the latter vv^as formed the ccelam, or body cavity 

 (vermiform stage, protuchous or aproctous). Next was 

 developed the notochord in a form related to the existing 

 ascidian and amphioxous larvK. The vertebral character 

 being thus attained, our ancestors passed through stages 

 now represented by the lampreys and the sharks, during 

 the ages which ended the archaeolithic period. While 

 the Devonian, Carboniferous, and Permian formations 

 were taking place, the Amphibian stage was passed, and 

 the succeeding development in the Trias epoch was from 

 this to a protamniotic form, distinct from that which gave 

 birth to the sauropsidan stem, and leading directly to the 

 mammalian. When the last strata of chalk had been 

 laid down, a marsupial form was changing into one now 

 represented by the lemurs. Lastly, the Tertiary period 

 witnessed the development of various gradations of 

 catarrhine Prinrates, from one of which the earliest men 

 directly sprung. 



The genealogy thus constructed (which is almost 

 exactly the same as those Prof. Hsckel has before pub- 

 lished) is plausible enough, and if such speculations 

 come under what the late M. Elie de Beaumont called 

 '■ la science mousseuse," they certainly have their use 

 in directing and stimulating inquiry. But is this the 

 way to introduce the results of biology to a popular 

 audience ? 



In the first place, the theory of evolution itself is 

 neither so certain nor so complete as persons who take 

 their knowledge from these lectures alone would be led to 

 suppose. Our author is astonished at Rutimeyer's com- 

 parison of "Darwinism" to a religion. But as held by 

 its illustrious author and by the ablest biologists both 

 in Germany and England, it is very much like a rational 

 theology : for it is a theory which only pretends to be a 

 more or less probable explanation of facts, which is held 

 liable to correction from fresh facts and with tolerance for 

 less probable explanations. But in these lectures evolu- 



tion is no longer a reasonable belief, but a fanatical and 

 intolerant Ahcri^laube. 



Again, granting that evolution by some means has 

 taken place, and that natural selection is a true cause of 

 evolution, it is not the only cause. Modifications of it, 

 like the so-called " Mimicry" of Bates and Wallace, have 

 already been discovered, and no doubt others will be. 

 The effect of Sexual selection, a struggle for existence of 

 the race as distinct from the individual, would not have 

 been guessed had not Mr. Darwin himself proved it : and 

 it often modifies the working of Natural selection. 



Lastly, if we accept evolution and so-called materialism 

 in its widest sense, the logical results will not be what 

 Prof. Hzeckel assumes. For these, like all other scientific 

 theories, deal only with secondary causes ; and when we 

 have traced back mind and matter alike to cosmic vapour, 

 the question still recurs, to what was that matter with its 

 potential functions due 1 In Protogcnes, or in the im- 

 pregnated human ovum. 



The thread of Life untwisted is 



Into its first consistences. 



Yet the mysteries of growth, of movement, and of genera 

 tion are not less but more mysterious than when less 

 nakedly exposed in higher organisms. Scientific investi- 

 gation, in the hands of Darwin, Fritz Miiller, Dohrn, and 

 Haeckel, has told us much and will tell us more of how 

 this world has come about ; but when men cease to 

 inquire into its final cause, the human race will have 

 made a step back towards its primordial slime. 



Leaving these general considerations, one is reminded 

 by Prof. Hffickel's attempt at a human philogeny of the 

 many fallacies which beset the application of the general 

 theory of evolution to this particular instance. 



When the dogma is accepted that " ontogeny is a re- 

 capitulation of philogeny," we find that the individual 

 development of man and his ancestors is far from com- 

 pletely known. The embryology, for instance, of Mono- 

 tremata and the Ganoids, including Ceratodits, is a blank. 

 Only the other day Mr. Balfour's admirable observations 

 on the development of sharks came to disturb what 

 seemed to be a universal law of vertebrate embryology, 

 and the origin of the urogenital organs is still confessedly 

 obscure. Yet Prof. Haeckel, while candidly admitting 

 this last difficulty, practically assumes one and not the 

 best-supported view to be correct. On the strength of it 

 he teaches that the kidneys are homologous with seba- 

 ceous glands, with the segmental organs of Annulata,* and 

 with the water-vascular canals of other worms ; and that 

 sperm-cells belong to the exoderm, germ-cells to the endo- 

 dqrm. Again, the placental classification which forms 

 the basis of the genealogical tree on p. 493 has been 

 always open to grave objection, and has now been de- 

 cisively contradicted by the researches of M. Alphonse 

 Milne-Edwards and Prof Turner. 



Again, even when the development of an animal is fully 

 made out, it is often so abridged and distorted an epitome 

 of its ancestry, that we may easily interpret it wrongly, 

 and we have at present-no signs to tell us when the clue 

 begins to fail. 



But a third and still more serious difficulty in con- 

 structing philogenies is the well-known incompleteness 



* Whether this ingenious hypothesis of pegenbaur will be confirmed on 

 other grounds i?, of course, a different question. 



