ytme 6, 1889] 



NATURE 



125 



knowledge it may be regarded as impossible that any one 

 person can have an equal knowledge of all the groups 

 into which the animal kingdom is now divided ; and 

 while at once acknowledging the care which has been 

 shown in the compilation before us, one has only to study 

 the chapters on the Plathelminthes and Vermes to find 

 how the author's special and great knowledge of these 

 groups has made this the most valuable portion of the 

 present part. The Protozoa are divided into three classes — 

 the Monera, Sarcodina, and Flagellata ; among these last, 

 such genera as Pandorina, Stephanospheera, and Volvox 

 are included without a hint being given that many regard 

 them as plant forms. The Coelenterata are divided into the 

 Gastraeadae, Porifera, and Cnidaria, and the former class 

 is made to include not only the Orthonectida: and 

 DicyemidiE, but also the Physemaridee. In the quoted 

 literature on this group no reference is made to Prof. Ray 

 Lankester's very impartial paper on a species of Hali- 

 physema. These facts are referred to, not as criticisms on 

 this valuable addition to an already large list of introduc- 

 tions to a study of the comparative anatomy of the 

 animal kingdom, but rather as in their way indicating 

 the standpoint from which this one has been written. 

 The printing is excellent, and the style of the work is 

 worthy of the house of Gustav Fischer, of Jena. 



A Manual of Practical Solid Geometry. By William 

 Gordon Ross, Major R.E. (London : Cassell and Co., 

 Limited, 1888.) 



This book follows in the main the lines of geometrical 

 drawing as studied at the Royal Military Academy, Wool- 

 wich. It will be found to be a useful help to those who 

 desire to have the power of producing accurate and work- 

 manlike drawings. Orthographic projection of points, 

 lines, and planes, system of vertical indices, and projection 

 of curves and solids, are first dealt with, and are followed 

 by simple cases of regular solids and solids of revolution, 

 illustrated by drawings in elevation and plan. A series 

 of solid geometry problems are next worked out 

 on the index system, figures being drawn in the more 

 difficult cases. Problems in connection with irregular 

 surfaces, and relating to the defilade of works of fortifica- 

 tion, are worked out, and also illustrated by drawings. 

 The appendix contains a collection of examples of differ- 

 ent kinds, and various hints and suggestions useful for 

 draughtsmen. 



Key to Lock's Elementary Trigonometry. By Henry Carr, 

 B.A. (London : Macmillan and Co., 1889.) 



The examples given in this book are fully and clearly 

 worked out, and in the elementary examples the author 

 has added considerable detail to enable those reading the 

 subject for the first time, and those who are studying it 

 without the help of a teacher, to obtain a clear insight 

 into the working of them. Great care seems to have been 

 taken to insure accuracy, and from beginning to end 

 a teacher would find it hard to add much in the way of 

 supplementary explanation. 



LETTERS TO THE EDITOR. 



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

 pressed by his correspondents . Neither can he undertake 

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

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. ] 



AbnormaUty in Tropseolum. 



In the early summer of last year my attention was directed to 

 a case of abnormality in flowers of Tropseolum, which I think is 

 sufficiently interesting and rare to be worthy of record. 



I observed three distinct plants of several years' growth (in a 

 conservatory) to be producing flowers in consideral'e numbers 



which were peculiar in having the spur either completely or 

 partially invaginated, as shown in the figure. 



In examples where the invagination is complete, the intruded 

 spur occupies the exact position of the stamens, and it is a fact 

 of some significance that it is not uncommonly double. 



Flowers of the normal form were also developed, and I 

 noticed that as the summer advanced the proportion of these 

 increased until eventually the plants produced only flowers of 

 the ordinary kind. They are again flowering this season, and 

 are repeating their behaviour of last year in every detail. 



I am not aware of any similar case having been recorded either 

 in Maxwell Masters's "Vegetable Teratology" or elsewhere. The 

 facts brought to light by the examination of numerous examples 

 seem to me to suggest a new interpretation of the nature of the 

 "spur" in this flower, which I purpose discussing at a later 

 period. In the meantime I shall be very glad to hear of 

 any similar instances either in this or any other "spurred" 

 flowers. Alfred Denny. 



Firth College, Sheffield, May 27. 



The Structure and Distribution of Coral Reefs. 



In reply to Mr. Guppy's letter permit me to state that (owing 

 to Captain Wharton's kindness) I had before me, when writing, 

 the Report on the Survey of the Tizard and Macclesfield Banks. 

 That reef-building corals occasionally grow at depths con- 

 siderably greater than 25 fathoms was already known (see 

 "Coral Reefs," second edition, p. 115, note), and Commander 

 Moore's investigations did not appear to me to do more than 

 confirm this. Mr. Guppy, I think, must have read his copy of 

 the Report rather hastily, or he would hardly have failed to quote 

 the following "suggestive remark " which occurs on p. 16: — 

 "This fact [a living astrrean at 45 fathoms] proves that the fine 

 sand of the lagoon is not necessarily fatal to the solid reef-building 

 astrsean, and helps to explain how individual coral heads appear 

 in the deep waters of these atolls, V>ut it cannot be doubted that 

 their growth is very limited. . . Coral growth is most luxuriant 

 between 2 and 12 fathoms." T. G. Bonney. 



Atmospheric Electricity. 



Not once only, but on several occasions, I have been alarmed 

 by the fizzing of my ice-axe in the Alps. 



Twice in one neighbourhood — the RifTelberg — I have been 

 in company with several tourists who have (as I myself) been 

 considerably frightened. 



It must be remembered that the Riflelberg and the Corner 

 Grat contain so much iron as to affect the compass observations 

 of surveyors. How often may this be a determining cause? 



Alpine Club, May 28. ^Marshall Hall. 



