February 15 iqi2] 



NATURE 



511 



ing the omission of practice in the application of the 

 physical laws. These difficulties the author has to a 

 large extent surmounted by adding to each chapter 

 a series of worked examples, thus avoiding the intro- 

 duction of them into the text. Interest is undoubtedly 

 added to the subject by the historical setting, and 

 it is quite possible that students may be induced to 

 regard physics with more favour on account of it. 

 The printing is good, but the diagrams are neither 

 so numerous nor so well produced as they might be. 

 As evidence of the lack in this respect, not one of the 

 four methods of determining the velocity of light is 

 illustrated diagrammatically. 



(4) The most surprising feature of Dr. Clay's book 

 on practical light is the fact that considerable 

 space is devoted to pin optics. The size of the book 

 suggests that its scope will cover experiments of a 

 much more elaborate character. This is indeed found 

 to be the case, repetitions by more accurate methods 

 of the rough pin determinations being described at a 

 later stage. As a result the book appears unequal, 

 and the omission of the pin experiments would have 

 been a gain rather than a loss. The ground covered 

 is very extensive, particular attention being paid to 

 the chapters on the compound lens, the microscope 

 nnd colour, on account of the importance of their 

 industrial applications. Colour, especially, is treated 

 much more fully than is usually the case in text- 

 books of practical physics, and the numerous experi- 

 ments described in this connection add considerably 

 to the value of the book. The diagrams with which 

 the experiments are illustrated are exceedingly good, 

 so much so that a student, having here before him 

 the perspective view of the arrangement of apparatus, 

 could scarcely fail to set it up correctly without other 

 aid. It may also be pointed out that, with the excep- 

 tion of one, all the diagrams have been specially pre- 

 pared for this work. The general arrangement of the 

 experiments is normal and logical, and the two 

 appendices, containing useful practical hints, are very 

 desirable. In short, notwithstanding the rather un- 

 fortunaTe inclusion of pin optics referred to. Dr. Clay's 

 book will certainly form a very useful reference work, 

 not only for students of physics, but also for those 

 engaged in industrial applications of the principles of 

 light. 



INDIAN FRESH-WATER INVERTEBRATES. 

 The Fauna of British India, including Ceylon and 

 Burma. Edited by Dr. A. E. Shipley, F.R.S. 

 Fresh-water Sponges, Hydroids, and Polyzoa. By 

 Dr. N. Annandale. Pp. viii+251+v plates. Pub- 

 lished under the authority of the Secretary of State 

 for India in Council. (London : Taylor and Fran- 

 cis ; Calcutta : Thacker, Spink and Co. ; Bombay : 

 Thacker and Co., Ltd.; Berlin: R. Friedlander & 

 Sohn, 191 1.) Price 105. 

 '"PHIS volume differs in some important respects 

 -L from those that have preceded it in the " Fauna 

 of British India." It is the first of the series to be 

 written entirely in India, and since, as the author 

 very justly remarks, "biological research on Indian 

 animals can only be undertaken in India," it is only 

 NO. 2207, VOL. 88] 



fitting that a large part of the volume should be 

 devoted to observations on the bionomics and life- 

 history of the organisms dealt with. It is thus far 

 more than a merely systematic monograph, and con- 

 tains a great deal that is of interest and importance, 

 not only to the special student of the Indian fauna, 

 but also to the general biologist. 



The Indian region is especially rich in fresh-water 

 sponges. Thirty-six species, subspecies, and varieties 

 are enumerated (including three added in the appen- 

 dix), although on p. 51 the number is given as only 

 twenty-nine, possibly because of doubts as to the 

 systematic or geographical status of some of the 

 forms. Of these no fewer than twenty-two have been 

 discovered and named by Dr. Annandale, who, how- 

 ever, pays a generous and well-merited tribute to the 

 pioneer work in this field of the late Dr. H. J. Carter, 

 of Bombay, 



Little is yet known as to the seasonal cycles 

 in the life-histories of fresh-water animals living under 

 tropical conditions, and on this subject Dr. Annandale 

 has many interesting observations. He points out 

 that in temperate regions the approach of winter 

 affects most of the less highly organised inhabitants 

 of fresh waters in the same way, leading to the pro- 

 duction of gemmules, statoblasts, and the like, which 

 lie dormant during the unfavourable season. In India, 

 on the other hand, the reaction to seasonal changes 

 is by no means identical, even in closely allied species. 



"Some species flourish chiefly in winter, and enter 

 the quiescent stage at the beginning of the hot weather 

 (that is to say, about March), while others reach their 

 maximum development during the ' rains ' (July to 

 September), and as a rule die down during winter, 

 which is the driest as well as the coolest time of the 

 year." 



A striking example of specific idiosyncrasy in this 

 respect is given in the case of two sponges, Spongilla 

 bomhayensis and Corvospongilla lapidosa. found in 

 Bombay. They 



"resemble one another considerably as regards their 

 mode of growth, and are found together on the lower 

 surface of stones. In the month of November, how- 

 ever C lapidosa is in full vegetative vigour, while 

 S hombayensis, in absolutely identical conditions, is 

 already reduced to a mass of gemmules, having 

 flourished during the 'rains.'" 



The Hydrozoa dealt with consist only of two species 

 of Hydra Dr. Annandale's important discovery of a 

 fresh-water medusa (Limnocnida) in streams of the 

 Western Ghats (Nature. August 3. 19") having come 

 too late to be included in this volume. One of the 

 species of Hydra is the familiar and widely distributed 

 H vulgaris, and Dr. Annandale has much that is new 

 to tell regarding the bionomics even of this much- 

 studied animal. Especially interesting is the account 

 of the way in which the larva of a small midge. 

 Chironomus fasciatipennis. preys upon Hydra. The 

 larva which protects itself with a tubular case of silk, 

 entangles the Hydra with a silken thread, and binds 

 it firmly to the outside of the tube, to be afterwards 

 devoured at leisure. . 



Of Polyzoa about sixteen forms are recognised. 

 One of the most interesting is Hislopia lacustris, 



