428 INSECTA. 



This class of animals, respecting external figure, and also respecting 

 their animal economy, may be divided into two kinds ; for instance, the 

 spider, louse, &c. may be put into one class, and those that go through 

 changes, or fly, into another. This latter is the class I here mean to 

 treat of ; and, as they undergo several changes before arriving at per- 

 fection, I shall call them the metamorphosing insects 1 . The other class 

 have all their parts gradually formed, from the first formation to its 

 most perfect state ; this I believe to be the case with the spider, 

 lobster, &c. 



For the first class I shall keep the term ' insect,' as it has been long 

 applied, and become familiar. 



Most insects belong to a country where there are seasons ; and such 

 as live [through the year] I believe sleep during the winter, excepting 

 the common bee. "Where they do sleep is not fully known. One would 

 suppose, and I believe it is commonly observed, that severe winter kills 

 many insects, and that mild winters preserve them ; and this is known 

 by the numbers that come forth in the spring or summer following ; 

 but contrary to this general rule was the effect of the mild winter in 

 1789 and 1790, for there were fewer insects of all kinds in the summer 

 of 1790 than I had ever seen 2 . This may have arisen from the mild- 

 ness of the spring bringing them forward too early, and then a few cold 

 days coming on killed them, as it did the blossom of the fruit trees. 



This class of animals is perhaps as remarkable an instance of the 

 play of nature, as any that we find in the animal world ; and it is prin- 

 cipally owing to the changes they undergo. 



The most perfect animals that we know of undergo a change which 

 divides their life into two stages, in which there is a considerable differ- 

 ence in the economy of life. For this purpose, the formation of some 

 parts are altered or lost, and others are consequently put into use ; but 

 these parts are but very few in number. All the adult parts are 

 regularly forming while the animal is still in the womb or in the foetal 

 state ; in which state it has a few parts not to be found in the second 

 stage. These chiefly respect the circulation, and of course the mode of 

 nourishment; as, e. g., the ductus arteriosus, ductus venosus, and 

 foramen ovale, which fits the foetus for the way of life it is then in. 

 The human is one of the instances of this kind. The life of the foetus, 

 in such, being very different from what it is afterwards ; therefore, the 

 above-mentioned parts become soon obliterated upon the commencement 

 of the new life ; in which the lungs are put into play, and the sensitive 



1 [Answering to the Metabolia of Leach, MacLeay, &c.] 



- [The effect here noticed is rather the rule than the exception.] 



