Feb. 15, 1872] 



NATURE 



299 



pleased to have finished this new edition, in which the 

 breach is complete." The contents of the book show 

 that this is no half-hearted conversion. 



It is divided into chapters, each of which treats of the 

 anatomy of one of the primary groups of the animal 

 kingdom, and the following table of contents, not given 

 in the work itself, sufficiently indicates the principles on 

 which the arrangement is made, i, Protista and Pro 

 tozoa ; 2, Coelenterata ; 3, Echinodermata ; 4, Vermes ; 

 5. Arthropoda ; 6, Mollusca ; 7, Tunicata ; 8, Vertebrata. 

 There is a good account of the Tunicata, or " Primeval 

 A'ertebrates " (Urwirbelthiere), from which the following 

 is an extract. 



After describing the characters of the ascidian larva 

 as known before Kowalevsky's researches, the author 

 continues : 



" When the yelk-division has taken place, the ovum 

 becomes first flat and then hollow on one side. A 

 depression is thus formed, lined by two layers of cells 

 (germinal lamina;). From the more superficial of these 

 are developed the skin and nervous system, from the 

 deeper the notochord, muscle5, and alimentary canal, the 

 muscles arising in a secondary layer of cells derived from 

 the deeper original one. A dorsal groove bounded by 

 two longitudinal folds becomes rapidly converted into a 

 tube, the spinal canal, and this is immediately followed by 

 formation of the tadpole-like tail. . . . The primitive 

 digestive tract is the depression described above, which first 

 closes and then forms a new opening on to the surface, the 

 future mouth. The branchial sack, alimentary canal, and 

 cloaca keep pice with the other organs (those, namely, 

 which are derived from the superficial or serous layer), 

 and when the larva becomes fixed, the latter either dis- 

 appear altogether, like the notochord, or undergo retro- 

 grade change, like the nervous system. Thus the original 

 likeness of the larva to the vertebrate type becomes lost." 



Each chapter begins with a pretty full survey of the 

 classes, orders, and other sub-divisions in the group of 

 which it treats, with their s^iveral characters. In looking 

 through these, some points appear worthy of note. No 

 mention is made of Gregarinida. Sponges are kept 

 among the Protozoa. The account of this class is not so 

 full as might have been expected from the author's 

 familiarity with it ; and with respect to its relation 

 to the Ccelenterata, he merely remarks : " The early 

 form of calcareous sponges, as well as the adult condi- 

 tion of certain genera, suggest a comparison with the 

 Coelenterate type." The Tunicata are removed from 

 the worms, but Infusoria are added to this heterogeneous 

 group, which, with Prof Schmidt and most German 

 naturalists, includes Bryozoa and Annulata, and probably 

 contains as many distinct types as it did when Linnseus 

 first defined it. Among the Arthropoda, Limulus is 

 placed between the Amphipoda and Branchiopoda, as 

 the type of the Crustacean order Poscilopoda. while 

 the Myriopoda do not appear at all. The Pteropoda 

 form an order of the Gasteropoda, or (as they are 

 inconveniently called) Cephalophora. The Vertebrata 

 are divided into seven classes, Atnphioxus and the 

 Cyclostomi being both separated from Pisces, and made 

 into independent primary divisions. Dipnoi appear as 

 the highest order of fishes, separated from the Ganoids 

 by Teleostei. Among the monodelphous mammals it is 

 surprising to see the Sirenia still united in the same order 

 with the true Cetacea ; while, on the other hand, the 



Pinnipedia are separated from the other Carnivora. The 

 order Primates is broken up by the exclusion of Homo 

 altogether, and the separation of the Lemurs (Prosimias). 

 The author agrees with Haeckel and Gegenbiur in regard- 

 ing this last order as the lowest of the Discophorous 

 Mammalia, and as representing the ancestors of that 

 group. . 



The morphological description in each of the above 

 chapters embraces in most cases too wide a subject for 

 the space allotted to it. Even in Gegenbaur's work one 

 finds the Vertebrata, and still more the Vermes, too ex- 

 tensive for the anatomy of the whole group to be con- 

 veniently considered at one view, and, not only is 

 Schmidt's style less concise, but is not illustrated by 

 diagrams of any sort. The account of the vertebrate 

 skull and of the specialisation of the somites of Arthro- 

 poda are instances of the deficiency referred to. More- 

 over, there is generally much too cursory an account of 

 Embryology in comparison with other subjects. Indeed 

 the development of Vertebrata is entirely omitted. The 

 bibliography is evidently intended as a guide for students 

 to the latest and most accurate works in each department 

 and for that purpose is fairly complete and well selected ; 

 but there are some remarkable omissions, as of Mr. 

 Parker's monograph on the shoulder girdle. 



On the whole, this expanded syllabus is interesting, as 

 a fresh instance of the progress which " the new zoology " is 

 making abroad ; but its chief practical vaUie will probably 

 be to thoie who have the advantage of hearing the 

 author's lectures. For thsm the wish with which he sends 

 out the present edition will no doubt be amply fulfilled : 

 " I hope that it will remain what it has been, a book for 

 students, and will keep me in that active intercourse with 

 young minds which ensures to a university teacher the 

 freshness of thought, the imagination and openness to 

 new ideas, which he can so ill afford to Ijse." 



P. H. Pye S.mith 



OUR BOOK SHELF 



Text-Books of Science. Technical Arithmetic and Men- 

 suration. By Charles W. Merrifield, F.R.S. (Long- 

 mans and Co.) 



Arithmetic is a science as well as an art, and although 

 the title of this book points solely to the art of arithmetic, 

 we are bound to examine how far it has supported its 

 right to a place in the scries of text-books of science. 

 The author says in the preface that " his experience has 

 led him to believe that there is not much practical con- 

 nection between successful teaching and logical sequence. 

 The province of logic is to test ideas, not to impart them." 

 We venture to demur entirely to these propositions, and 

 to assert that each successive idea acquired by the pupil 

 should be made to follow logically from the ideas pre- 

 viously existing in the mind, and that ideas which cannot 

 stand the test of logic are, in an educational point of view, 

 worthless. 



We proceed to select a few instances of the disregard 

 of logical sequence which the author considers compatible 

 with successful teaching, (i.) The only definition of di- 

 vision given is the following : — " The object of division is 

 to find how many times one number is contained in 

 another. This number of times is called the quotient." 

 A few pages further on is given the method of dividing 

 /. s. d. by 365, and no hint is given that a different inter- 

 pretation of division is required, viz., distribution of the 



