332 Analysis of Scientific Books. 



plunged under water, it appears as if cased in silver, or some 

 bright metallic covering ; this appearance being evidently derived 

 from a stratum of hair, interposed between its body and the sur- 

 rounding liquid. This down not only serves to repel the adhesion 

 of any moist substance to its body, but also facilitates the motion 

 of the animal, by lessening the degree of friction which would 

 otherwise take place ; and it is owing to the same circumstance 

 that there is an unusual degree of difficulty in retaining a sure 

 hold of the insect, even when dead ; but more especially when 

 alive, and struggling against detention. The degree of force which 

 it commonly exerts on such occasions is very remarkable, and, 

 from the sensation produced, may easily be supposed to be what 

 Rosel says it is, equal to the counterpoise of two or three pounds. 

 The skin or covering of the insect is in some parts nothing more 

 than a thin membrane ; in other parts it resembles soft leather ; 

 and sometimes equals horn, or even shell, in its degrees of hard- 

 ness. 



The mole-cricket is more distinctly divisible than most other 

 insects into three separate parts, the head, the thorax, and the 

 abdomen. Of these, the head is not above one-twelfth the length 

 of the whole body ; the thorax three -twelfths ; and the abdomen 

 eight- twelfths. 



The head is united to the thorax, as the thorax also is united 

 to the abdomen, by means of a loose membrane, which envelops 

 the muscles that pass respectively from one to the other ; and it 

 is in consequence of the looseness of these membranes that the 

 animal is enabled either to separate the connected parts to a con- 

 siderable distance from each other, or to contract them so closely 

 together as to hide the interposed membranes from view ; and, 

 from the arched form of the anterior part of the thorax, it can 

 draw in its head under that part, much after the manner of a 

 tortoise. The same flexibility of the connecting membranes 

 enables the animal to place either its head or its thorax at a 

 considerable angle with the rest of the body ; a movement 

 which is very characteristic of this insect, and gives it an air 

 of intelligence ; the attitude being apparently that of watching 

 or listening. 



Dr. Kidd next proceeds to a detailed account of the structure of 

 the external parts of the insect, and enumerates some curious and 

 interesting particulars respecting its general anatomy. Upon the 

 recondite subject of the sanguineous circulation of insects, our 

 author throws out some new and important hints which deserve 

 the attention of naturalists, and especially of the comparative 

 anatomist. 



" In meditating on this difficult problem," says Dr. Kidd, " it 

 lias forcibly occurred to me, that the trachese may possibly be 

 the instruments of such a circulation ; absorbing the blood or the 



