1898] SOME NEW BOOKS 125 



the antennae and mandibles. The outer skeleton of the thorax is 

 described in detail, and the account of the structure and modifications 

 of the legs and feet is specially full and suggestive, being accompanied 



by an excellent summary of the mechanics of insect limbs a n ed for 

 walking, climbing, and swimming. This is mainly derived from 

 Graber's work, supplemented by later researches. Like most 

 American zoologists, Prof. Packard is inclined to allow much weight 

 to the effect of use, disuse, and mechanical pressure in bringing about 

 modifications in limbs. There is even reference to the strange 

 opinion that the absence of tarsal segments from the front legs of 

 certain digging-beetles is a character acquired by frequent mutilation 

 and now become hereditary. In the account of the wings, there is no 

 comparative view of the venation in various orders of insects. There 

 is, however, a good summary of what is known of wing-development 

 both in the lower and higher (metabolous) insects. Prof. Packard 

 rejects the once fashionable theory that insect-wings are modified 

 tracheal gills, believing that they originated in some purely terrestrial 

 form: but he considers it likely that the folds of skin whence they 

 were derived had originally a breathing-function. He agrees with the 

 orthodox view that the elytra of beetles are modified front wings, 

 rejecting their identification with the tegulae of Hymenoptera as 

 suggested by Meinert and Hoffbauer. Xot only the cerci and stvlets, 

 but also the paired external genital organs are regarded as true 

 appendages of the abdomen. The section on the outer form of insects 

 concludes with an account of such outgrowths of the skin as tubercles, 

 hairs, spines, and scales, and a chapter on insect coloration, the 

 latter dealing rather with the physical and chemical than with the 

 bionomie aspects of that wide subject. 



The portion of the book on the internal anatomy and physiology 

 of insects commences with an account of the muscles, followed by a 

 chapter on the nervous system, in which the author accepts Yiallanes' 

 threefold division of the insect brain, copying many of his figures, 

 while a well-selected series of figures from Brandt illustrates stages in 

 the fusion of the ganglia of the ventral chain. The histology of the 

 nervous system is dismissed somewhat briefly. On the other hand 

 the sense organs are fully dealt with, and a clear summary of the 

 conflicting views of various naturalists on the method of insect vision, 

 and the functions of dubious antennal structures is valuable ; but there 

 is only a mere mention of the ear in the basal antennal segment, de- 

 scril ied 1 >y Hurst and Child. The comparative anatomy of the digestive 

 tract is full and well illustrated, and is followed by a short account of 

 digestion and secretion. Then the salivary and spinning glands, 

 urinary tubes; wax-glands, repugnatorial scent, and poison-glands are 

 dealt with. The author is not inclined to follow Brauer in attaching 

 importance to the number of urinary tubes as showing the relationships 

 of the insect orders. The accounts of the circulatory, respiratory and 

 reproductive systems are excellent ; especial care is given to the minute 

 structure of the breathing-tubes, the comparative morphology of the 

 genital ducts, and the formation of the germ-cells. 



The section on embryology is mainly drawn from the work of 

 Korschell and Heider, and is illustrated by copies of their figures, 

 so that it forms a valuable introduction for English students to the 



