SCIENTIFIC LITERATURE. 



567 



times, and he indicates the possession 

 of something like 50 additional forms. 



Almost 100 pages are devoted to the 

 peculiarities of mosquitoes in all ^ 

 stages, and to the methods to be era- ! 

 ployed in studying them. The mouth : 

 structures are explained in the con- 

 ventional way and the matter of food 

 is gone into somewhat in detail. Of 

 course comparatively few mosquitoes 

 ever get a meal of blood, and yet it 

 would seem that for some species such 

 a meal is an essential preliminary to 

 reproduction. All sorts of vertebrates 

 may be attacked, even fish and reptilia, 

 and invertebrates seem almost as sus- 

 ceptible. The males, being unable to 

 puncture either animal or vegetable 

 tissue, are confined to a diet of pre- 

 pared liquids — nectar and the like — 

 but do not despise others, like beer and 

 wine, when they can get them. 



To mosquitoes as disease carriers 

 only a few pages are devoted; the 

 author referring to such writings as 

 Eoss's, Grassi's, Nuttall's and others. 

 He specifically discusses ' Malaria,' 

 filariasis and yellow fever, though 

 adding nothing from personal observa- 

 tion. Birds and probably some animals 

 suffer from diseases carried by these 

 insects and usually only one, or a small 

 group of species, acts in the transmis- 

 sion. Thus the species of Anopheles, in 

 America at least, is responsible for the 

 distribution of malarial troubles, while 

 Siegomyia appears to do as much for 

 yellow fever. 



Mr. Theobald emphasizes the char- 

 acter of the scales on certain por- 

 tions of the head, wing and body, 

 which assists in separating species. 

 This brings into play the microscope 

 and, practically, that instrument must 

 be resorted to for final determinations 

 in some instances. 



It is altogether a very interesting 



and useful book to the entomologist 

 who wishes to learn what has been 

 done in this family and who has dono 

 it. The plates are too highly colored 

 and the figures are, therefore, mislead- 

 ing. The text figures, illustrating 

 structural details, are as a whole only 

 fair, though the point to be illustrated 

 is always well brought out. The book 

 maker's work is well done, and so is the 

 printer's, while a good index adds 

 materially to the facility with which 

 the book may be used by the reader. 



MECHANICS. 



An 'Elementary Treatise on Theoret- 

 ical Mechanics' by Professor W. Wool- 

 sey Johnson (Wiley and Sons, New 

 York) is far from elementary, as the 

 reader is supposed to have a good 

 knowledge of differential and integral 

 calculus. The laws of nature are, how- 

 ever, quite independent of any system 

 of mathematics, and many of those dis- 

 cussed in this volume might be easily 

 treated by elementary algebra and 

 geometry. There can be no objection 

 to the use of the calculus if its demon- 

 strations are simpler than those of com- 

 mon methods, but the combination of 

 difficult mathematics with difficult sub- 

 ject-matter should be avoided in an 

 elementary text-book. The plan of the 

 book is that usual in this subject, forces 

 being discussed at much length, in con- 

 nection with the time-rate of space or 

 velocity, before the subject of work or 

 energy is taken up. This plan follows 

 the historical line of development, but 

 it is questionable whether it is the best 

 method for the student or for getting 

 at practical solutions. The book con- 

 tains no unsound doctrine, is concisely 

 written in a scholarly tone, and is an 

 able presentation of the subject imder 

 the plan adopted. 



