April 13 1899] 



NA TURE 



557 



-physics and chemistry in the remaining part of the book. 

 Electricity is dealt with in sixteen pages of this part, and 

 chemistry in twenty-eight pages. Most of the illus- 

 trations are line drawings, and will not be attractive to 

 the young people for whom the book is mtended ; for few 

 natural history objects can be well represented by out- 

 line sketches, and children often have a difficulty in un- 

 derstanding them. 



In the preface the editor, referring to the object of the 



book, suggests that it should be especially useful in "the 



junior classes in schools." But few teachers who have 



' had experience in giving instruction to such classes would 



approve of the order in which some of the subjects are 



' dealt with. For instance, the first chapter deals with the 



' difficult subject of classification of animals, and leaving 



' out of account the fact that the scheme of classification 



■ described is somewhat old-fashioned, we think it peda- 



' gogically wrong to begin the study of natural history 



I by classifying the animal kingdom. Teachers may, 



however, find the volume useful in providing information 



' for lessons on natural history objects, and suggesting 



experiments in physics and chemistry. 



I Notes from a Diary in Asiatic Turkey. By Lord 

 I Warkworth, M.P. Pp. xvi -t- 268. (London: Edward 



Arnold, 1S98.) 

 I The author of this book, now Earl Percy, travelled by 

 I several of the main routes and some unfrequented ways 

 of Asiatic Turkey in 1897. He shows himself to be a wide- 

 awake politician, an instructed antiquarian, and something 

 of a sportsman ; hence the narrative necessarily deals with 

 matters from a point of view somewhat remote from the 

 scientific The book is charmingly got up, gracefully 

 written, and illustrated by some choice reproductions of 

 good photographs, one of which represents a dervish 

 with a dagger thrust through both cheeks and ap- 

 parently insensible to pain. Throughout the journey, 

 indeed, there seems to have been very little objection 

 on the part of the people to allow themselves and their 

 belongings to be photographed, a result doubtless of the 

 infiltration of Western ideas even into the remoter parts 

 of the Turkish empire. Incidentally, one or two points 

 of scientific interest are touched upon. The strange 

 idea is noted that the honey of a district near Erzeruni 

 is not only poisonous when taken in large quantities, 

 but that if the red water-melon is eaten at the same 

 meal with some of the honey, death would result from 

 the formation of large crystals in the stomach. A 

 curious statement is made as to the extent of the occa- 

 sional inundations of Lake \'an, one of the natives 

 declaring that the water had recently risen as much as 400 

 feet, a degree of tlood which the author prudently views 

 as an exaggeration. The discovery of a spring "bubbling 

 over with a copious flow of liquid sulphur" (p. 204) would 

 certainly be interesting, but it probably was no more 

 than water impregnated with sulphuretted hydrogen. 



As an intelligent, modest, and serious account of an 

 interesting journey in a country still difficult of access, 

 this book deserves very hearty commendation, and it 

 would be gratifying to believe that all members of 

 Parliament could make so good a use of their holidays 

 as Lord Percy has done. 



Lectures on Theoretical and Physical Chemistry. By 



J. H. van 't Hoff. Translated by R. A. Lehfeldt. Part 



I. Chemical Dynamics. Pp. 254. (London : Edward 



Arnold.) 



To what has already been said regarding the French 



edition of this e.xcellent work (X.^TURE, p. 458) there is 



little to add. The translation is accurate, the few slips 



that occur being mostly referable to the original, and 



easy of detection. As to paper and printing the book 



leaves nothing to be desired, although perhaps this result 



has been attained at the expense of a wider popularitywhich 



the book might have enjoyed had its price been lower. 



NO. 1537, VOL. 59] 



LETTERS TO THE ED/'JOR. 



The Editor doe! 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. 

 Mo notice is taken of anonymous communications.} 



Experiment to Illustrate the Zeeman Effect. 



Prof. A. Gray has kindly called my attention to his Royal 

 Institution lecture of April 29, 189S, in which, nearly a year 

 ago, he pointed out the analogy between a pendulum with a 

 gyrostat in its bob, and the molecule of a gas vibrating in a 

 magnetic field, which I called attention to in my recent letter 

 (p. 509). Geo. Fras. FitzGerald. 



Trinity College, Dublin, April 5. 



Formation of Egg-capsules in Gasteropoda. 



The function of the sole-gland of the foot in certain divisions 

 of the Gasteropoda seems hitherto to have remained unknown. 

 None of the works I have been able to consult give a definite 

 account of the function of the organ. This .sole-gland appears 

 from the literature to exist only in the dioecious Azgygobranchia, 

 whereas the more anterior marginal gland of the foot is found 

 both in these and in Pulmenata and Opisthobranchia. 



On the other h.and, I have been unable to find any published 

 account of the origin and formation of the horny capsules, in 

 which the ova of most Azgygobranchia are deposited and con- 

 tained during their development. Many writers seem to assume 

 that these capsules are formed in the generative duct, which is 

 not the case. 



I have recently satisfied myself that these two gaps in our 

 knowledge of the MoUusca are really one ; in other words, that 

 the egg-capsules are formed by the sole-gland, and that the 

 latter is really the nidamental gland. I first discovered this in 

 the common whelk Biicciniim undatum, which I found in 

 numbers in the act of spawning on the shores of Falmouth 

 Harbour in November 1897. Pulling away the animals from 

 the stones to which they adhered, I found incompletely formed 

 capsules in the cavity of the sole-gland, and saw that the 

 "spawn"' was formed and deposited by the "foot." The ova 

 are probably transferred to the cavity of the gland, before the 

 closure and deposition of the capsule. I have recently verified 

 the same fact in the s.ame locality in another species, namely 

 Murex erinaceus. In this case the capsule is long and narrow in 

 shape, and I saw it in an imperfectly matured though fully 

 formed condition, drawn out of the aperture of the sole-gland, 

 when I detached a specimen in the act of spawning. 



Lacaze Duthiers has shown that the float of fanthina is 

 formed by a glandular depression of the foot corresponding to 

 the sole-gland, and Johannes Thiele maintains that the egg- 

 capsules of this animal, attached to the float, are produced also 

 by a certain portion of this gland. Simroth, however, believes 

 with Lacaze Duthiers that the "cocoons" or capsules are 

 derived from the sexual organs. I have no doubt Thiele is right, 

 but he does not appear to have extended his doctrine to other 

 forms than Janthina. 



The function of the sole-gland being thus established, the 

 question arises whether there is not a diflisrence in the structure 

 or size of the gland between the male and female, since the male 

 does not produce egg-capsules. This and other questions I 

 must leave to be investigated in future. Not knowing when I 

 may have leisure to make a more detailed study of the subject, 

 I wish to make known the main fact, which can be easily 

 verified by the observation of living Prosobranchs in the act of 

 spawning. J. T. Cunningham. 



I Morrab Terrace, Penzance. 



The Natural Prey 01 the Lion. 



What constitutes the natural prey of the lion in his wild state 

 is, I believe, a disputed point. The majority of people, probably, 

 are of opinion that he is extremely fastidious in his tastes ; 

 others, again, assert that he will eat almost anything. Certainly, 

 it is only reasonable to suppose that a lion sufficiently under the 

 impulse of hunger will eat "almost anything" I 



Years ago I was present on more than one occasion when 

 animated discussions on this point took place between two 

 notable African ecclesiastics — both since dead— Bishop Smythies 



