NA TURE 



605 



THURSDAY, APRIL 25, 1901. 



KORSCHELT AND H EIDER'S EMBRYOLOGY. 



Text- Book of the Embryology of Invertebrates. By Profs. 

 Korschelt and Heider. Translated by M. Bernard. 

 Vol. ii., 1899 (pp. XV + 375) ; Vol. iii., 1899 (pp. xii + 

 441); Vol. iv., 1900 (pp. xi + 594). (London: Swan 

 Sonnenschein and Co., Ltd.) 



"\ X /"E welcome with great satisfaction the publication 

 * * of Parts ii., iii. and iv. of this important work. 

 Originally issued in German in three parts, the first two 

 of which were reviewed in these columns in 1891 

 (vol. xlv. p. 145), the English translation was issued in 

 four parts, the first of which was published in 1896, the 

 second and third in 1899, and the fourth part in 1900. 

 In the somewhat considerable interval which has elapsed 

 between the issue of the original work and that of its 

 English translation, extensive additions have been made 

 to our knowledge in several departments of embryology. 

 These have been met by editorial footnotes and supple- 

 mentary lists of literature. The latter appear to have 

 been carefully compiled and will be found by students to 

 have great utility. Indeed, it may be said that, so far as 

 the literature is concerned. Parts ii., iii. and iv. are up 

 to date, and there can be no question that they will be of 

 the greatest value to English zoologists. All that was said 

 in praise of the work m the review of Part i. (Nature, 

 1896, vol. liii. p. 361) applies with almost greater force 

 to the volumes before us. They constitute an accurate 

 and comprehensive treatise on invertebrate embryology, 

 and no zoologist's library can be considered complete 

 without them. 



The work of the translator and editor also appears to 

 us to have been excellently carried out. The style is 

 clear and the work in its English form is eminently read- 

 able. We congratulate the editor upon his sensible 

 decision to translate the German word " anlage" by its 

 English equivalent, "rudiment," and we entirely agree 

 with his remarks in the preface to Part i. on the subject. 

 In opposition to him, however, we think that his restoration 

 of the word "rudiment" to its proper use in embryology 

 will satisfy, if not all zoologists, at least all intelligent 

 zoologists. The word has no biological application outside 

 embryology. In embryos alone can we actually see 

 the first rough outline gradually shaping itself into the 

 perfect organ ; and there can be no question that we are 

 dealing with a rudiment. But the same cannot be said 

 when the word is applied to organs of the adult. These 

 undergo no change, except retrogressive changes ; and 

 to apply the word "rudimentary" to them implies the 

 possession of prophetic power. We mean, if we apply 

 the word " rudimentary" to an adult organ, that in some 

 remote descendant of the animal under consideration the 

 organ will become more perfect as the result of evolu- 

 tionary change. This is an entirely gratuitous assump- 

 tion, which we have no right seriously to make. The 

 word " vestige," the use of which our editor also dis- 

 cusses, is on a very similar footing. It may be 

 NO. 1643, VOL. 63 J 



appropriately applied to organs which undergo regression, 

 after having attained a more perfect structure in the earlier 

 phases of growth, but do not totally disappear ; but it 

 cannot legitimately be applied to adult organs on any 

 other condition. For to call an adult organ, which has 

 not undergone such regression, " vestigial," implies a 

 knowledge of the past, which we have not got, just as 

 rudiment, when applied to adults, implies a knowledge of 

 the future. It may be that the small and imperfect 

 muscles of the outer ear of man are vestiges of more 

 perfectly developed muscles in a remote ancestor, but we 

 have no knowledge that they are so ; this view of them 

 is a mere presumption, based on no fact whatsoever. To 

 apply the word " vestigial " (unless the above-mentioned 

 condition be satisfied) or "rudimentary" to adult organs 

 is merely to beg the question at issue, and we require 

 another word to apply to organs which we may feel 

 tempted to designate in that manner. The same remark 

 applies to those organs of the embryo like the neurenteric 

 canal or gill slits of vertebrata, which make their appear- 

 ance in development but give rise to no structures in the 

 .later stages or adult. 



As a general rule in German works, the treatment of 

 ccelom and body-cavity is not up to date. Our authors, 

 we are glad to see, ai-e not open to serious blame in this 

 respect, but they have not been able entirely to shake 

 themselves free of traditional conceptions with regard \.o 

 these structures. They constantly make use of the 

 words pseudocode, primary body-cavity, secondary body- 

 cavity, which all belong to a past epoch of morphology ; 

 and they sometimes use language which might lead the 

 reader to suppose that they do not distinguish clearly 

 between hasmoccele and ccelom (iii. 90). Moreover, in 

 dealing with cases in which the nephridia are actually 

 transformations of the ccelom in the ontogeny, they speak 

 of them as though they were really only secondarily 

 related to it (iii. 205). But, in spite of this, it must be 

 admitted that their ideas on these subjects are more 

 advanced than has been usual with German authors. 



As was stated m the review of Part i. of this work, the 

 standpoint of our authors is that of the seventies and early 

 eighties of last century. This is clearly seen in their dis- 

 cussions on ancestral derivation, in their chapters on 

 general considerations (which, in our opinion, are too long 

 and often somewhat tedious) ; in their treatment of the 

 layer-theory, in spite of such statements as those given on 

 p. 301 of Part iv., by which it is shown that the central 

 nervous system arises from ectodermal rudiments which 

 also give rise to mesoderm ; in their frequent inability to 

 accept observations which depart at all from traditional 

 conceptions, as witness their treatment, on pp. 166 

 and 169 of Part iii., of Sedgwick's observations on the 

 cleavage and derivation of the enteron of Peripatus 

 capensis. We do not make these remarks in any way to 

 detract from the merit of our authors' work. Morpho- 

 logy is at present in a transition state, and naturalists 

 do not readily part with the old hopes and beliefs which 

 fired them with so much enthusiasm in the early 

 Darwinian days and spurred them on to make those 

 comprehensive researches of which this book is such a 

 worthy record. 



