1898] SOME NEW BOOKS 125 
the antennae and mandibles. The outer skeleton of the thorax is 
deseribed in detail, and the account of the structure and modifications 
of the legs and feet is specially full and suggestive, being aceompanied 
by an excellent summary of the mechanics of insect limbs as « sed 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. Not only the cerci and stylets, 
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 
bionomic 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 Viallanes’ 
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- 
scribed by 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 
Korschelt and Heider, and is illustrated by copies of their figures, 
so that it forms a valuable introduction for English students to the 
