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[February 20, t8q6 



method followed. And surely no greater praise could 

 be given to it. Not only is the method of treatment 

 almost identical, but the points of view from which the 

 facts are looked at is almost exactly the same as that 

 adopted by Balfour more than fifteen years ago. The 

 passage — " In the group Metazoa or germ-layer animals, 

 on the contrary, there always results a multicellular 

 organism (cell-community or cell-corm), in which the 

 single cells give up their independence for the good of 

 the community, and accommodate themselves to a division 

 of labour, in consequence of which there is brought about 

 a diversity in the structure and function of the cells of 

 the Metazoan organism" (Introduction, p. i) — shows 

 that the cell-theory in its modern form is the key-note 

 of the work, and that the germ-layer hypothesis of Huxley 

 and Kowalevsky still holds the prominent position as- 

 signed to it in Balfour's work. And we are very far 

 from blaming the authors for thus adhering to the old 

 faiths of the seventies ; for though much may now be 

 urged to diminish the importance of these hypotheses, 

 which in their day have done yeoman's service to the 

 furtherance of anatomical science, and though it might 

 be argued, as has lately been done in more than one 

 quarter, that they are moribund and powerless to lead 

 us further in the intricate task of unravelling structure, 

 still it would be foolish, to say the least of it, to cast 

 them on one side m a didactic work of this kind, until 

 some better, some more penetrating guide has been 

 found to replace them. 



After this, it is hardly necessary to say that it is our 

 opinion that the authors are men of sound judgment, a 

 fact which is shown in every chapter of their work. But 

 we have said enough to indicate our admiration for the 

 work. The authors are scholars in the best sense of the 

 word. Their erudition is profound, their accuracy is 

 minute, their industry and patience must be marvellous, 

 and their critical powers are quite first-rate. In sound- 

 ness and impartiahty their judgment leaves nothing to 

 be desired. So far as our knowledge goes, credit is 

 always well apportioned, and conflicting statements are 

 handled, if not with the consummate skill of Balfour, 

 still in a manner which is unusual in works of the kind. 



The volume before us is part i. of the German work, 

 and deals with the Porifera, Coelenterata, Platyhel- 

 minthes, Nematelminthes, Annelida, Echinodermata, 

 Rotifera, Cheetognatha and Enteropneusta, treated en- 

 tirely in a systematic manner. 



Parts ii. and iii., of which a translation is promised, 

 complete the treatment of the invertebrata. In the 

 authors' preface, a general part is spoken of, but so far 

 as we know it has not yet appeared ; and the vertebrata 

 are expressly excluded from the scope of the work. This 

 omission we hold to be a defect. The authors defend it 

 on the ground that that department of the subject has 

 been adequately treated recently by other hands. We 

 entirely differ from this view ; for not only do we hold 

 that no entirely satisfactory treatment of the vertebrata 

 has appeared since Balfour's work, but that no satisfac- 

 tory treatment is possible apart from the rest of the 

 animal kingdom. Moreover, though the phylum verte- 

 brata is only one phylum of the animal kingdom, no 

 scientific treatment of the subject as a whole is possible 

 without at least a consideration of the facts of vertebrate 

 NO. 1373, VOL, 53] 



embryology. One might as well, in a scientific treatise 

 on chemistry, omit all reference to carbon and its com- 

 pounds. We sincerely hope that the authors will change 

 their minds, and will, when they issue the general part,, 

 append an account of vertebrate embryology. 



In a work of this magnitude there must be a certain 

 number of small mistakes and slips ; but we have found 

 surprisingly few of them. We might, however, cal 

 attention to two, which bear on subjects having a certain 

 amount of general interest. On p. 3, it is stated that 

 the "ectoderm germ-layer presides over the animal 

 functions (sense, perception, locomotion)." This is of 

 course an error ; for not only are the most important 

 muscles often endodermal in origin, but, if certain 

 observations are to be trusted, it is highly probable that 

 the main nervous tracts arise in situ in the mesoderm. 

 On p. 31, a series of diagrams showing the structure of 

 the canal-system in certain sponges is described as "a 

 diagram of the development of the canal system in 

 various sponges." This is obviously a loose statement. 

 What the authors probably mean is, that the diagrams 

 illustrate various conditions of the canal-system, which 

 are actually met with in different sponges, and which 

 may be supposed hypothetically to represent permanently 

 stages of structure through which the more complicated 

 canal systems have passed in phylogeny. This slip is 

 of more importance than at first sight it may appear tO' 

 be, because phylogenetic speculations, if they are to have 

 any value at all, and not to be mere hindrances, must be 

 described in the most precise language, and based upon 

 the most exact ideas. It is very important at the present 

 time, when so many loosely-conceived and worthless 

 phylogenetic hypotheses are constantly being put for- 

 ward, that the necessity for precision and clearness of 

 thought at least should be regarded as indispensable in 

 all attempts to trace the ancestry of living animals. 



With this one exception, which is obviously a slip, this 

 volume is happily entirely free from all blemishes of the 

 kind. The phrase, " embryonic connective tissue," though, 

 no doubt sanctioned by usage, is one to which we take 

 exception. The tissue so described has almost, if not: 

 quite always, nothing whatever in common with connec- 

 tive tissues as ordinarily conceived, but is a germinal or 

 growing tissue which gives rise to most important organs. 



The translators have performed their task with skilL 

 There are short notices, made for the most part by the 

 authors, of the more important memoirs which have- 

 appeared since the publication of the original in 1890. 

 The German idiom is quite got rid of, and the book in its 

 English form is eminently lucid and readable. The trans- 

 lators are to be congratulated on their work, and have 

 earned the gratitude of all English zoologists. But, alas 1 

 there is one serious blemish. If the translators were 

 Englishmen, we should call it an error of taste ; but being. 

 Americans, we must make allowances, and put it down as 

 another example of the curious incompleteness of their 

 knowledge of the English language, which some Ameri- 

 cans are known now and again to display. We all know 

 how frequently the word Milage is used in German works 

 on embryology ; and we all know that some authors,, 

 notably those writing in America, refusing to use the 

 English equivalent, have attempted to add this word to 

 the English language. The translators of this work have 



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