290 Mono'ir vpon the compound 



by prolonging itself afterwards into two cordons, which form new 

 ganglions, from which other nerves is»<ue wliolly as if from the 

 brain. But in the injects, wc know that tliere exist as manV 

 ganglions as there are vings, while in the true araclnioides this 

 number is alwavs far less con^^itle:•able. Besides, in the articu- 

 lated animals, tiic nervous system in general undergoes few vari- 

 ations ; it even shows in an evident manner, that all these ani- 

 mals have been formed on one and the same i)lan, which has 

 merely undergone «)me trifling modifications adapted to peculiar 

 circumstances. 



From what we have observed, there will be some changes ne- 

 cessary in the classification of the articulated animals, and the 

 class of insects will l^e better distinguished from that of the 

 arachnoides than it has been hitherto ; for these animals differ 

 from each other in their organs of respiration and circulation, 

 and even, although in a manner less striking, in those of repro- 

 duction and nutrition. Tliis branch of the subject will form a 

 separate memoir, on the organs of circulation and respiration of 

 somefamiHes of articulated animals. In the mean time we shall 

 observe, that the arachnoides aie divided naturally enough into 

 two principal families, the oviparous arachnoides and the vivi- 

 parous arachnoides. It is besides very singular, to find this 

 mode of gestation in animals whose organization is also very 

 simple ; for their system of respiration may be assimilated, undor 

 certain points of view, to that of some crustaceous decapodes 

 with long tails : as to their circulation, it is purely pulmonary. 

 The division of the arachnoides which we have mentioned, is, as 

 we see, very different from that hitherto adopted ; indeed this 

 division will fall of itself to be still more subdivided, in order to 

 place each genus in the most natural order. In this classifica- 

 tion the arachnoides will always come after the crustacece ; but 

 the order in which the insects have been usually arranged must 

 te totally inverted. Thus, instead of terminating the series of 

 insects bv the apterce, as several naturalists have done, we must 

 on the contrary commence with them, since most of the apterce 

 have a greater affinity with certain arachnoides. 



The common sjiiders haviiig ramified respiratory organs or 

 tracheae, and being thereby deprived of an organ of circulation 

 furnished with vessels, are true insects; I ought, therefore, to say 

 a few words with respect to their eves. 



Tlie eyes of the phaLangium are situated nearly like those of the 

 crustacece, with vvhich the common spider has besides some rela- 

 tions, either from the disposition of theirbodics,andoftheirorgan» 

 of movement, or, finally, by the volume of their hepatic vessels, or 

 their livers. Thus, the position of the smooth eyes of the common 

 spider (noothersar* observediu tliis genu*) is considerably different 



Irom 



