108 



SCIENCE. 



[N. S. Vol. V. No. 107. 



(1) " So far as has yet appeared, this theory 

 (of antithetic alternation of generations in 

 Metazoan development) rests upon the author's 

 observation that the epidermis contributes, in 

 early embryonic stages, to the production of 

 nerve cells. The transformations of these cells 

 he has not followed,^' etc., (2) "hence the whole 

 embryo is a transient structure," etc. 



(3) ' ' The author discourses at length upon 

 the well-known fact that in all vertebrates 

 there is an embryonic period, at the close of 

 which the anlages of all the principal organs 

 are present, but not yet diiferentiated." 



(4) ' ' We have been unable to see that the 

 elementary facts, which the author has collated, 

 are anything more than what is commonly 

 taught beginners in embryology, (5) nor to 

 recognize that they afford any arguments to 

 support the author's theory of 'antithetic 

 alternation.' " 



As regards the heading 1, the reviewer is 

 apparently unaware of the existence of the 

 completed part of my work published in April, 

 1896, in the Zool. Jahrb. under the title, ' The 

 history of a transient nervous apparatus in 

 certain Ichthyopsida — an account of the de- 

 velopment and degeneration of ganglion cells 

 and nerve-flbres.' 



The work contains some of the results of six 

 years' investigation of the matter ; it was carried 

 out on upwards of 120 embryos (out of a collec- 

 tion of 500 or more), whose sizes ranged from 

 5 mm. to 19 cm., and it is illustrated by 8 

 double plates containing more than 131 figures. 

 I assert, and challenge your reviewer to prove 

 the contrary, that in the work in question the 

 whole of the transformations of these cells to their 

 complete degeneration are described, illustrated 

 and established. I have asked many compe- 

 tent embryologists what was their opinion on 

 this point, and not one of them expressed any- 

 thing but the conviction that I had completely 

 established the transient nature of the ganglion 

 cells. Hence I conclude that the reviewer 

 must have been dreaming when he wrote ' ' it 

 may be questioned whether a failure to study 

 the fate of certain cells in an embryo is a suffi- 

 cient basis to construct a revolutionary theory 

 upon." When I wrote my work upon them I 

 had only studied them for six years ! 



(2) No such foolish idea as that mentioned 

 in the review, to wit, that ' the whole embryo is 

 a transient structure,' has ever entered my head 

 as any time. What I believe, and what I have 

 written more than once, is that there is in the 

 development of every vertebrate a more or less 

 reduced larva or 'phorozoon' of a transient 

 nature, that an embryo or sexual generation 

 could be transient has never yet occurred to 

 myself, or to anyone else, so far as I am aware. 



(3) This is supposed to be a criticism on what 

 I have discribed as the ' critical stage ' or phase. 

 The reviewer considers that there is no new dis- 

 covery in this, but he adduces no evidence for 

 his belief, that it is ' a well known fact, ' and 

 that what I have brought forward is nothing 

 more than what is taught beginners in embry- 

 ology. 



If it be a well-known fact, this existence of a 

 corresponding period in the development of 

 vertebrates, and (4) if the facts I have described 

 be such as are usually taught beginners in em- 

 bryology, surely there must be evidence of it in 

 some of the text-books of embryology. There 

 is certainly no evidence of this ' well-known 

 fact ' in the literature of embryology, beyond the 

 few lines I have cited from His regarding the 

 human embryo, and, although I am pretty well 

 acquainted with the more important current 

 text-books, I have never been able to find any- 

 thing in any of them, not excluding Minot's 

 volume, bearing on the matter. 



Why, moreover, within the past few years, 

 should Keibel and Oppel, who are well versed 

 and skilled, working and teaching embryolo- 

 gists, have spent so much time and labor in 

 searching for corresponding phases in embryos 

 of different vertebrates, and why should they 

 have failed to find my critical phase, if it were 

 already known to exist? Founding on these 

 researches and my own, I state that there is 

 only one such corresponding phase in the de- 

 velopment and that it was first described in the 

 pamphlet under consideration. If your re- 

 viewer questions the truth of this, let him pro- 

 duce his evidence. I believe, and the contrary 

 has still to be proved, that my pamphlet con- 

 tains the following novelties, fate of the yolk, 

 yolk-sac and merocytes, discovery of a corre- 

 sponding critical phase in the development of 



