December 1, 1892.] 



KNOWLEDGE 



23B 



of whom it should be welcome as summarizing present 

 knowledge and indicating the advantage, and indeed neces- 

 sity, of co-operation between students in different branches 

 of science. Much loss has hitherto accrued to science in 

 consequence of the lack of such co-operation. The ento- 

 mologist, it is true, describes and identities his insect 

 accurately enough, but when he comes to the fungus which 

 has spoilt his specimen he has nothing but loose and vague 

 terms for it, and fails to hit upon its characteristic features, 

 so that the mycologist cannot recognize the systematic 

 position of the plant from his description ; and on the other 

 hand, the botanist, while careful enough in working out 

 the life-history of his fungus, is too apt, through lack of 

 interest, to go astray in his entomology, and fails to identify 

 his insect, or even sometimes does not so much as deter- 

 mine the order to which it belongs. Such a book as this 

 ought to do much to remedy this defect, showing as it does 

 the imperfection of much existing knowledge, and indi- 

 cating the gaps which only co-operation can fill up. In 

 the body of the work the claims of the student of insect 

 Ufe seem at first sight to be most prominently recognized, 

 the hosts which sutler from fungoid parasites being treated 

 under their respective orders systematically ; further on is 

 added, for the special benefit of the lover of these lowly 

 plants, a classified list of the fungi, including a mention of 

 their several hosts. To the majority of readers it will no 

 doubt be news that there exists material enough for the 

 compilation of a substantial volume of three hundred and 

 fifty pages on such a subject as this. Few persons except 

 specialists are acquainted with more than two or three 

 kinds of parasitic fungi. There is first the minute form 

 that is so destructive to house-dies, gluing their bodies to 

 the window panes, walls, or chandeliers, while it surrounds 

 the corpses with a sort of whitish halo. Most good 

 museums, again, contain specimens of certain New Zealand 

 or Tasmanian caterpillars fi'om whose bodies project a long 

 horn-like fungus sometimes to the length of several inches. 

 Then there is the species which has earned notoriety by 

 the extent to which it has touched the pockets of a certain 

 section of the commercial world, viz., the celebrated 

 muscardine, which for many years created immense 

 mortality amongst silkworms. - But when we have enu- 

 merated these we have probably almost reached the 

 Umits of popular knowledge ; yet Dr. Cooke enumerates 

 some two hundred species which have already been 

 described as preying upon insects and spiders of different 

 kinds, and this he is able to do without entering at all, 

 except to the extent of the single species that causes 

 the so-called " foul brood" amongst bees, upon the broad 

 field of investigation connected with the minute bacilli 

 and bacteria, which play so important a part in respect of 

 the well-being of both animal and vsgetable life. Parasitic 

 fungi attack insects in very different ways. Of course a 

 dead insect will be subject, like all other organic matter, 

 to the growth of moulds, which would probably be of the 

 same species as those that appear on other corpses. But 

 it would be hardly justifiable to call these parasitic, and 

 therefore it is specially with those that attack living 

 insects that our author is concerned. Here the fungus 

 may merely use the insect as a basis of support and be 

 simply attached to its exterior, thus apparently doing little 

 harm ; or it may become a much more insidious enemy by 

 penetrating the body, forming its vegetative portion or 

 mycf'Utuii at the expense of the tissues of its host, and 

 ultimately bursting through the skin for the formation of 

 its reproductive portion externally. Much depends upon 

 the habits of the insect ; those that live in close or damp 

 situations, beneath the ground, or in burrows in trees, are 

 more liable to attack than those that lead an exposed life. 



The maturation of the fungus, Dr. Cooke maintains, does 

 not take place till all the interior of the host has been 

 absorbed, and it has therefore succumbed. It is only in 

 this condition, when the spore-bearing receptacles have 

 been developed, that the characteristic features of the 

 fungus are exhibited, and its specific determination becomes 

 possible. Before suffering its fate, the insect, as it finds 

 its end approaching, often climbs into some conspicuous 

 position, clinging with a death-grip to a leaf or stem of 

 grass ; while it remains in this attitude, the fungus passes 

 through its skin, and by its own growing threads attaches 

 the corpse firmly to the substratum on which it rests, 

 while the spores, when developed, find themselves in a 

 suitable position for being conveyed away by the wind to 

 do destruction elsewhere. Dr. Cooke figures various kinds 

 of ants, bees, wasps, beetles, and other insects that have 

 thus become the soil out of which grow branching threads 

 or club-headed columns, by which, in some cases, the 

 appearance of the insect is so greatly modified as to have 

 given rise to the name " ^'egetable Wasps." The perusal 

 of this book will serve to impress vividly upon the mind 

 that the dangers to which insects are exposed during their 

 life by no means all arise from the animal world, but that 

 the vegetable kingdom supplies foes quite as insidious and 

 quite as deadly as any that arise from other sources. 



Bivtics, Ihittirdies, Moths, ami other Insects. By A. W. 

 Kappel and \V. E. Kirby (CasseU & Co.). — The authors 

 have catered for beginners in entomology, and for those 

 who, while not professmg to be students of the science, 

 yet like to know something about the common insects to 

 which a visit to the country introduces them. They have 

 produced a book of reference which, while it makes no 

 great demands upon either the purse or the time, gives the 

 sort of information such readers require, as to structure, 

 habits, collection and preservation. Between four hun- 

 dred and five hundred selected representatives of the seven 

 principal orders are briefly described, those, as a rule, 

 being chosen, and wisely so, which are either the 

 commonest or have some special point of interest in their 

 economy. An analytical table for determining the order 

 to which an insect belongs is a useful feature which will be 

 much appreciated by beginners, who are often puzzled as 

 to the nature of their captures. About one hundred and 

 seventy species are figured in twelve coloured plates, which 

 are generally well executed, though with a little tendency 

 to gaudiness, and in our opinion the tinted ground on 

 which they are printed is hardly an improvement. 



Utttcrs. 



•-•-* 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 

 t ♦■« 



ox THE IMPERFECTION OF OL'R KNOWLEDGE OF 



THE SPECIES OF INSECTS. 



To the Editor of Knowledge. 



Deai; Bia, — Few persons, even among entomologists, 

 have any idea of the vast numbers of insects which exist, 

 or of the immense gaps in our knowledge of even the 

 largest and most conspicuous groups. In the introduction 

 to the new edition of my " Elementary Textbook of 

 Entomology" I have estimated the number of species 

 already described at '270,000, and the actual number of 

 existing species is variously guessed at by different authors 

 at from two to ten millions. Even at the former figure, 

 which I must admit appears to me far too low, it was 

 calculated by Lord Walsiugham, in his notable address to 

 the Entomological Society of London, in .January, 18iJ0, 



