352 THE WATER-BEETLE. 



insects, whether in the perfect or the larva state, 

 and such a practice would rather be an anomaly in the 

 case of insects that deposit their eggs, or have their 

 early stages of life in the water. The threads are 

 always discharged from the body of the insect in the 

 state of a viscid fluid, which acquires consistency the 

 moment that it comes in contact with the air ; and, 

 therefore, until it is actually seen, we are not prepared 

 to admit that a similar operation could go on in the 

 water. The plunger is, indeed, so far analogous to 

 the coleoptera, that inhabit the land, that it cannot 

 remain under water without coming up to breathe ; but 

 even that would not justify for it the imputation of a 

 power which was to be exercised in the water, and 

 which yet was not in accordance with the general laws 

 of the inhabitants of that fluid. 



Upon most subjects, the only danger of gross error 

 lies in too hasty a generalization ; but in the study of 

 natural history, and in no part of it more than the 

 adaptation of creatures to the element in which they 

 live or find their food, there is an opposite danger 

 generalizing too little. This is too much the case in 

 the history of insects. The particular creature, or the 

 particular habitis, taken apart, and one insulated fact 

 is put in succession to another insulated fact, not only 

 without any direct observation of the fact of invariable 

 sequence, but against that which appears to be a ge- 

 neral law. In the inhabitants of the air, including 

 those that cannot fly, as well as those that can (for the 

 air is the medium in which they all live), we find a 

 certain uniform organization, varied much in form, no 

 doubt, but uniform in principle. So very uniform, that 



