October 20, 1892] 



NATURE 



i85 



who, although they are unable to acquire any technical 

 skill in carrying out the operations themselves, should 

 have, nevertheless, an intimate knowledge of the principles 

 which they ought to embody. 



We think that more space should have been devoted 

 to that portion of the book which deals with drainage 

 proper. While nearly loo pages are given to lead-laying 

 and the jointing and bending of pipes, only about twenty 

 pages are devoted to house-drains, and a great part of this 

 is occupied with illustrations of appliances. Not more 

 than one or two pages are given to the subject of cast-iron 

 drains, although they are strongly recommended, and 

 the subject is a very important one. We trust, however, 

 that the author will remedy these deficiencies in the 

 future editions which will doubtless be required to supply 

 the demand for his excellent text-book. 



OUR BOOK SHELF. 



A Lecture Course of Elementary Chemistry. By H. T. 



Lilley, M.A. (London : Simpkin, Marshall, Hamilton, 



Kent and Co., 1892.) 

 The abrupt use of chemical terms, and the condensed 

 style adopted by the author in this book, make it evi- 

 dent that it is not specially designed to smooth down 

 the difficulties which confront the unaided learner who 

 approaches chemistry for the first time. It seems rather 

 to be fitted to replace the notes which might be taken 

 on a course of lecture instruction. Regarded in this light 

 it is a useful volume, the knowledge it contains being, in 

 the main, sound and to the point. 



It deals with the metals as well as with the non-metals, 

 and dovetailed with the ordinary chemical information 

 are many instances that the author has tried to keep pace 

 with current work, and has attempted to give the student 

 all the important points to be noted in a fairly complete 

 course of elementary chemistry. 



A short series of exercises chiefly in chemical arith- 

 metic are given at the end of the book, and a table of 

 contents and an index are supplied. 



It would be advisable on p. 53 to say that ordinary 

 sulphur crystallises in the rhombic system. To speak of 

 the crystalline form as an octohedron tends to create an 

 impression common among students, that ordinary sulphur 

 belongs to the cubic system. Fluorine was not made by 

 the electrolysis of liquefied hydrofluoric acid, but of a 

 solution of potassium fluoride in the acid ; the pure acid 

 is a non-electrolyte. 



It is hardly correct to state that calcium sulphate and 

 hydroxide are the only known examples of solids less 

 soluble in hot than in cold water ; calcium isobutyrate and 

 one of the thorium sulphates are additional instances. 

 On p. 98 the flame colorations of potassium and sodium 

 are confused, and brass seems to be omitted in treating of 

 the alloys of copper and zinc. J. W. R. 



Longmans' School Geogi aphy for North America. By 

 George G. Chisholm and C. H. Leete. (New York: 

 Longmans, Green, and Co.). 

 If Mr. Chisholm's well-known geographical text-book 

 was to be extensively used in the United States, it was 

 inevitable that it should be altered in a way which would 

 adapt it to the special needs of American schools. The 

 task was undertaken by Mr. Leete, and he has accom- 

 plished it with much skill and judgment. The parts he 

 has rewritten are those relating to America in general. 

 North America, and the United States. To these he 

 gives a prominence which was not necessary or desirable 

 for European students of geography, but which is no 

 doubt essential for learners on the other side of the 



Atlantic. The plan of Mr. Chisholm's book and the 

 spirit of its execution have both been maintained, and 

 the work ought now to be quite as useful in the New 

 World as it has already been in the Old. 



Garden Design and Architects' Gardens. By W" 



Robinson, F.L.S. (London: John Murray, 1892.) 

 The author of this book is firmly convinced that to clip 

 and align trees in order that they may " harmonise" 

 with architecture is " barbarous, needless, and inartistic." 

 He is in love with Nature's methods, and would give 

 them in gardens much freer scope than is accorded to 

 them by persons who like best a certain trimness and 

 formality. It is to be regretted, perhaps, that Mr. 

 Robinson deals with the subject in so polemical a temper, 

 but the cause for which he contends is good, and he 

 does excellent service by bringing out prominently what 

 has always been the essential principle of the best and 

 most characteristic kind of English landscape gardening. 

 The value of the essay is greatly increased by a number 

 of well-selected illustrations. 



LETTERS TO THE EDLTOR. 



[The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to rettirK, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE, 

 No notice is taken of anonymous comtnunications.\ 



The Alleged " Aggressive Mimicry " of Volucellce. 



In the course of a review (Naturk, October 6, 1892, p. 

 535) of a book, " Animal Coloration," by Mr. Beddard, Mr. 

 Poullon takes occasion to refer to a theory professing to eluci- 

 date the resemblance of Volucellce to humble-bees, &c. This 

 reference is occasioned by the suggestion of a counter-hypothesis 

 by Mr. Beddard. The view adopted by Mr. Poulton (" Colours 

 of Animals," 1890, p. 267) is that proposed by Kirby and 

 Spence, and subsequently alluded to by KUnckel d'Herculais 

 ("Organ, et Devel. des Volucelles," Paris, 1875) ^^d others; 

 but as Mr. Poulton makes no reference to these authorities he 

 may be assumed to accept the full responsibility. In the place 

 named he says: — "The boldness of these enemies sometimes 

 depends on the perfection of their di.sguise. Thus the larvae of 

 flies of the genus Volucella live upon the larvae of bees and 

 wasps. Volucella bombylans occurs in two varieties, which prey 

 upon the humble-bees Bonibus muscorum and B. lapidarius, 

 and are respectively like these Hymenoptera. The resemblance 

 is very perfect, and the flies enter the nests to lay their eggs." 

 Mr. Beddard (/. c, p. 225) criticizes the view that the fly 

 resembles the bee that it may with impunity enter the nest, and 

 proposes to look on the presence of the fly's larvas in the bees' 

 nests as akin to the presence of supposed " pets " in the nests of 

 ants. As Poulton points out, this suggestion leaves the original 

 difficulty of the likeness of the fly to the bee untouched. 



Having little interest in either of these speculations, which 

 seem fantastic and premature, it is with reluctance that I take 

 part in the discussion. The case, however, of V. bombylans is 

 not only interesting as a striking, and to us in England a most 

 accessible instance of the phenomenon of Mimicry, but as an 

 example of Variation it is almost unique among animals, while 

 among plants perhaps it is paralleled only by Darwin's famous 

 case of the peach and the nectarine. It is besides a case well 

 suited for experiment and close observation. The nests of sur- 

 face building bees may towards evening be lifted bodily, bees, 

 Volucella, and all, with a spit of earth, and transferred to a box. 

 This may be taken home and set next morning c.n a window-sill, 

 when on opening the box the bees will go on with their work 

 for the rest of the summer. If any one serks an opportunity of 

 honestly trying to get to the bottom of a case of Mimicry, 

 instead of speculating about it at large, he can scarcely find a 

 better case than this. The need for such observations is great, 

 for the account confidently given by Poulton, though according 

 well with his hypotheses, accords with the truth less well. 



In these circumstances it may not be out of place to give a 

 brief statement of the facts as they were established by entomo- 

 logists long ago. The Volucella are a small group of flies, con- 



NO. I 199, VOL. 46] 



