NA TURE 



:65 



THURSDAY, JULY 20, \i 



VER TEBRA TE EM BR YOLOG Y. 

 Vertebrate Embryology. By A. Milnes Marshall. 



(London ; Smith, Elder, 1893.) 

 "T^HIS is an eminently practical treatise, designed to 

 -»- assist the senior university student in his labora- 

 tory work so as to enable him to gain a thorough know- 

 ledge of the successive appearances of the embryos of 

 amphioxus, the frog, the chick, the rabbit, and man, 

 during their course of development from the egg to the 

 adult form. The student is supposed to pursue his 

 studies by the aid of the most modern methods, and he 

 has here placed before him by means of clear methodical 

 description and clever original drawings exactly what he 

 ought to see and identify in his series of microscopic 

 sections. The book will be extremely useful, as are the 

 author's other treatises, to all teachers and students of 

 biology. It should be pointed out that very consider- 

 able pains has been taken by Prof. Milnes Marshall to 

 give accuracy and reality to his statements. Especial 

 care has been given to the account of the embryology of 

 the frog, which is illustrated by admirable original 

 drawings and may be regarded as a critical revision 

 of the subject based upon original work carried 

 out by the author and his pupils. Most of the novel 

 features in the chapter on the chick are derived 

 from the work of Duval, but in the later stages of the 

 rabbit's development Prof. Marshall again relies on his 

 own observations and drawings. The account of the 

 human embryo is based upon that of Prof. His with some 

 judicious additions. 



I have said that the work is eminently practical, and 

 by that I mean not only that the book is one for the 

 laboratory, but that the author whilst giving the greatest 

 care to accuracy of statement and presentation of fact, 

 has dealt very little — I may even say has avoided deal- 

 ing — with theoretical questions of wide interest. An 

 introductory chapter in some thirty pages gives a brief 

 and general sketch of the structure of the animal egg, its 

 maturation, its fertilisation, the segmentation of the egg 

 and the germ layers, theories of fertilisation and re- 

 capitulation and the origin of sex, and then we settle 

 down to our " types." 



1 do not doubt that the plan of teaching by " types" 

 has its merits, and has served a very useful purpose ; 

 also I cannot doubt that the plan of describing all the 

 phases of an animal's growth (except the adult phase) in 

 order, one after another, has advantages, and perhaps 

 such descriptions constitute — -if such a study can really be 

 distinguished and recognised — what is known as " em- 

 bryology." But it becomes daily more obvious that the 

 histology, morphology, and physiology of th? organism 

 must also be considered and treated without regard to 

 the arbitrary separation of adult and embryonic con- 

 ditions, and without that exclusiveness which the selection 

 of "types" involves. Morpholo^jy is essentially com- 

 parative j it involves the consideration alike of embryonic 

 and adult structure, and must avail itself of the facts of 

 structure exhibited in any and all forms, without being 

 restricted to certain types. It is a consequence of the 



NO. 1 238, VOL. 48] 



method of treatment adopted by Prof. Marshall that 

 many interesting morphological problems are not dis- 

 cussed by him. It clearly was not his purpose to con- 

 sider these problems, but rather to furnish the student 

 with a sound basis of observed fact. At the same time 

 it is a little disappointing — on looking up, in the 

 successive chapters on frog, chick, and rabbit, 

 the account of the development of the urinary 

 and genital ducts — to find no discussion or decisive 

 statement on the author's part as to the morpho- 

 logical relation of these structures, or any suggestion as 

 to the explanation of the divergences in the develop- 

 mental history of the Miillerian and Wolffian ducts in 

 these "types" respectively, and in other vertebrates. 

 In a work on vertebrate embryology one might reason- 

 ably expect such a comparative treatment. Similarly, 

 the question of blastophore and primitive streak and 

 " sickle" is but lightly touched, whilst the conflicting and 

 bewildering accounts of the germinal layers of the 

 mammalian blastoderm are left without further remark 

 than that the account adopted from Rauber and 

 Kolliker, as to what takes place in the rabbit, " is difficult 

 to reconcile with the course of development in other 

 mammals ; and further investigation is much needed on 

 these points." It could not be expected that Prof. Mar- 

 shall should settle in the present treatise all the knotty 

 points of vertebrate embryology, but would it not have been 

 well had he pointed out in some detail the difficulties of 

 reconciliation to which he briefly alludes, and given some 

 indications of alternative solutions of the problems in- 

 volved ? These reflections are by no means to be regarded 

 as depreciation ; they are rather intended to illustrate 

 the special lines within which the author has confined 

 his treatise. These being given, it is not too much to 

 say that he has produced a most valuable, clear, and 

 masterly exposition of the known facts of the develop- 

 mental history of leading types of vertebrata. 



Before concluding I may venture to point out two 

 matters which might be amended in a new edition of the 

 book, as well as in the same author's " Practical Zoolog) ." 

 The word " stomatoda;um " occurs in several places. 

 There is no reason that I know of for altering* the more 

 elegant form " stomodKum '' in this way : the one is as 

 "correct" as the other. Being the father of the word 

 "stomoda;um" and its twin "proctodeum," I should 

 prefer that those who use it would not delude themselves 

 into the notion that I have inadvertently or ignorantly 

 omitted a necessary syllable in its composition. The 

 second matter is as to Prof. Marshall's figures of trans- 

 verse sections of adult Amphioxus (Figs. 12 and 13). 

 These require (and have for some time required) cor- 

 rection. The clear space below the black undulated line 

 representing the plaited epithelium of the ventral surface 

 of the atrium should be filled in with shading. It is not 

 a space, as it was at one time thought to be, but is a solid 

 mass of gelatinous connective tissue. Moreover, the 

 dotted area marked S in both the figures is not, as the 

 explanation of the figure has it, the cardiac aorta. The 

 space so marked is the sub-endostylarccelomic space, and 

 the cardiac aorta, which is a relatively small vessel lying 

 within it, is not represented in the figures at all. 



E. Ray LANkESTER. 

 N ■ 



