108 Memoir upon the compound 



and the same eye presents as many as fourteen thousand, as 

 Hooke observed in the l/belbtfce*. Nature has even sometimes 

 multipUed the number of the eyes themseh'es, and this number 

 seems to be always in the ratio of the size of these very eyes, and 

 the immoveabiHty of the parts in which they are situated. Thus, 

 when the compound eyes are entirely wanting, the number of 

 the fiat or simple eyes is greatlv increased, and certain species 

 have thus even six pair of eyes. This is observed in some of 

 the apterae, many of the larvae, and particularly in the spider. 

 Indeed, the latter should be separated from the insects, as Messrs. 

 Lamarck and Cuvier have already done ; for their organization 

 presents some very marked distinctions, and of the first import- 

 ance. In fact, the spider like the scorpion has a kind of huigs, 

 and consequently a real heart with blood-vessels ; Avhereas in 

 the real insect the organs of respiration are always ramified, and 

 the vascular system, or at least what has been taken for it, neve? 

 is. Sometimes, however, the eves of insects are not situated in 

 parts entirely immoveable, and certain species present a kind of 

 neck, which Comparetti f seems to have been the first to observe, 

 and which permits the head to execute a variety of movements. 

 This neck is very conspicuous in some of the carnivorous species, 

 which not being able to pursue their prey on account of the 

 disproportion of their organs of movement, require the faculty 

 of seeing to a great distance. This organization is very evi- 

 dent in the inniilh, the evipuin, and tlie inarilispa, in which 

 the head mav be directed to one side, or backward, aTul may 

 even be twisted almost round. It may be remarked in general, 

 that the eyes are the more convex and the more salient, the more 

 decidedly carnivorous the insect is, as the mobility of the parts 

 in which they are situated, ij always relative to the kind of life 

 and to the habitudes of the insect. In short, we never saw the 

 eyes of these animals present any kind of movement, and they 

 ahvavs adhere to the parts where they are situated, and conse- 

 quently are completely immoveable. 



The sight is exercised by insects l)y two organs very different 

 from those which perform this function in the vertebral animals 

 and the mo/lnici: they exhibit even very striking differences 

 from each other, as well in respect of their external conforma- 

 tion, as in their internal disposition. Some appear to be a larg-e 

 cluster of eyes united together, if we may so express ourselves, 

 and others exhibit one only. The former have been called com- 

 pound ei/eSy on account of their arrangement ; and the lattejr 



* Swamnierdiim, Biblia Natura; torn. i. p. 490. and Collection Acudemi- 

 qvty p. S23. Ilooke lias niven the eyes of the LibeUulis in his Micn>i^ra- 

 yliia, plates xxiii and xxiv, 



t Dinamica Aaimule, part i. p. 103 to 106. 



smooth 



