5o6 



NA TURE 



{March 29, 1888 



system to speak of field botany with utter contempt, as a 

 subject unworthy of notice. This is a very unfortunate 

 thing, for there are many most interesting questions 

 which can only be settled by field-observation ; and field- 

 observation is in itself a most important, and at the same 

 time a most enjoyable, side of biological training. The 

 same contrast also holds, although to a less extent, on 

 the zoological side. It is much to be hoped that we may 

 be able to correct this great error which has unfortunately 

 attended a healthy, and, upon the whole, highly beneficial 

 educational reaction. It is to be observed that the excel- 

 lent general descriptions of the types which form so im- 

 portant a feature of the work are in every way calculated 

 to avert this error. 



The most striking thing in the revised form of "Prac- 

 tical Biology " is the reversal of the old arrangement, so 

 that the student is now led to begin with a Vertebrate type, 

 and from this to work his way down to the lowest forms 

 of life, and from these, again, upwards to a type of the 

 flowering-plants. There is little doubt that such a change 

 will be met by conflicting criticisms. I believe, however, 

 that the majority of those who have had the widest expe- 

 rience of biological teaching, and especially those who 

 have instructed students in the first use of the microscope, 

 will heartily agree with Prof. Huxley's defence of the 

 alteration, in the preface to the revised edition. The 

 process by which a student first learns to see with the 

 microscope is almost like the education of a new sense- 

 organ suddenly conferred upon a mature organism. We 

 know that under such circumstances it would be a very 

 long time before the impressions conveyed by the new 

 organ could be harmonized with the well-known expe- 

 riences resulting from the stimulation of other organs. 

 Accustomed to judge of the shapes of objects by their 

 appearance in three dimensions, the student is suddenly 

 provided with a field of vision in which shapes have to be 

 nearly always inferred from the appearance of solid three- 

 dimensional objects when seen under conditions which 

 prevent them from being examined in more than two 

 dimensions at any one time. For it is a long time before 

 the student can accustom himself, by focussing at suc- 

 cessive depths, and by making the most of the limited 

 third dimension of depth which the high powers of the 

 microscope provide, to judge accurately of the forms of 

 objects. And the novel conditions under which a student 

 sees with the microscope effectually prevent him from 

 making the best of the impressions he receives. Thus, if 

 the section of a solid object presented the appearance of 

 a circle i inch in diameter, and if two other sections at 

 right angles to each other and to the first section pre- 

 sented the appearance of a rectangular figure 3 feet by i 

 inch, nearly everyone would readily infer that the shape was 

 that of a cylinder 3 feet long by i inch in diameter. But 

 precisely similar data, when presented in the field of the 

 microscope, do not readily lead the student to any defi- 

 nite conclusions as to the forms of objects, and in reality 

 a long course of discipline is necessary in order to make 

 him form any clear conception of the actual shape of the 

 object at which he is looking. I therefore think that it is 

 expedient to begin the course of biological teaching with 

 organisms which only require the use of a microscope 

 for the investigation of part of their structure, and thus 

 to gradually work downwards to the minutest organisms, 



in which the whole investigation depends upon high 

 microscopic powers. Thus the gradual training in the 

 use of the microscope will proceed parallel with its 

 gradually increasing necessity. 



The addition of the earthworm, the snail, and of Spiro- 

 gyra is a great improvement upon the former edition of 

 the work. If a choice were necessary, the snail is in 

 many respects a more suitable type than the Anodon. In 

 spite of the greater structural simplicity of the latter form, 

 the anatomical details are more difficult to demonstrate by 

 dissection and more difficult to see when dissected than 

 those of the snail. This objection to the Anodon of 

 course only applies to its selection in preference to the 

 snail in the earlier edition ; it is in every way desirable 

 that the Lamellibranchs, as well as the Gastropods, 

 should be represented by a well-known type. These 

 newly added types and the additions to the descriptions 

 of those in the previous edition, and to the practical direc- 

 tions, so increase the size of the volume that it contains 

 almost exactly twice the number of pages present in the 

 earlier form of the work. The practical directions given 

 in the appendix appear to be excellent, and to contain in 

 a very small compass an immense amount of information 

 upon the most recent and approved methods. There are 

 a few sHps and indefinite statements which should be 

 modified in succeeding editions, which will doubtless be 

 called for at no distant date. 



Thus, on p. 383 we are told that one or two per cent, of 

 the sugar is unaccounted for in fermentation ; but for the 

 rest it is only loosely stated that the greater part is 

 resolved into carbonic anhydride and alcohol and a small 

 part into glycerine and succinic acid. On pp. 384 and 

 386 it would be well to represent the numerical propor- 

 tions of the formulas by the same method. On p. 462 it 

 is wrongly stated that the cotyledons become green in the 

 type selected. They are in reality hypogeal. On p. 467 

 no phosphorus is mentioned in the culture solution in 

 which it is stated that the bean-plant will grow. It 

 should read : " potassium phosphate, iron sulphate," in- 

 stead of " potassium and iron sulphate." In the note on 

 p. 475, "discolour" is used for "decolorize." On p. 483 

 the student is advised to procure 2 ounces of microscopic 

 slides and half a gross of cover-slips ! 



Such slight errors can easily be put right, and they 

 would in most cases be detected by the student in reading 

 the book for the first time. They cannot be considered as 

 seriously detracting from so excellent a book, and one 

 which, in the extreme clearness of its style, is so 

 admirably adapted to the needs of the beginner. 



E. B. P. 



A TEXT-BOOK OF EMBRYOLOGY. 



Lehrbuch der Entwickelungs-geschichte des Menschen 



und der Wirbelthiere. Von Dr. Oscar Hertwig, 0.0. 



Professor der Anatomic und vergleichenden Anatomie 



der Universitat, Jena. (Jena : Gustav Fischer, 1886.) 



THE brothers Hertwig are highly esteemed as original 

 investigators in the field of embryology wherever 

 that science is cultivated. The completion of a systematic 

 work by one of them on the conventional lines of human 

 , embryology is therefore a matter of some moment. An 



