1S14.] On the Uses of the Dorsal Vessel. 349 



arachnides, such at least as it has been conceived by modem natu- 

 ralists. We have, on the contrary, restrained it to the cloportides,' 

 scorpionides, and arachnides. They have all an elongated heart, 

 with two orders of blood-vessels, and circumscribed respiratory 

 organs, composed of pyramidal leaves, exhibiting this remarkable 

 particularity, that they receive the air directly by stigmatiform 

 openings. But it is with hesitation that we have placed the clo- 

 portes among the arachnides. What we ki ow of their organization 

 pointed out that union so strongly that we have not ventured to 

 place them among the crustaceous animals, with which, however, 

 they have various relations. We have put the eloportes at the head 

 of the arachnides, and immediately after the Crustacea, in order to 

 point out the relation which exists between the first and last orders 

 of these two classes. We see that the cloportides constitute the 

 transition from the one to the other. By adopting this mode of 

 classification we have been obliged to begin the study of insects 

 with those species which have the greatest affinity with the spiders, 

 the last order of the arachnides. In this respect there was no diffi- 

 culty in making a choice ; the phalangites placed themselves, as it 

 were, of their own accord at the head of the insects. However, 

 fur a contrary reason, we have been obliged to separate the jules 

 and scolopcndra, which in some respects have an analogy with the 

 cloportides. In seeking for the arrangement which would the least 

 interrupt the natural relations which the articulated animals have to 

 each other, we were convinced that the characters drawn from the 

 organs most essential to life could not unite them in such natural 

 groupes as they do the animals with vertebras. This is one of the 

 great difficulties in their classification — a difficulty probably pro- 

 ceeding from the smaller influence which the organs of circulation 

 and respiration have in proportion as the organization becomes 

 more simple. 



We have thought it equally necessary to separate those insects 

 which undergo transformations from those which, like the arach- 

 nides, do not undergo any. We have divided the whole into two 

 great divisions, founded solely upon this transformation, which in 

 one division takes place by degrees, while in the other it operates, 

 as it were, instantaneously. In consequence of this great division 

 we have been obliged to form an additional order among the insects. 

 This order, which we have called syphon-aptera, connects very well 

 the injects that undergo a transformation with those that do not. 

 les, ir commences in a very natural manner the order of insects 

 that are suckers. These lead us to the other orders of suckers from 

 which we pass to the bruisers, which, being more complete insects 

 (if the term may be allowed), ought to be at the greatest distance 

 i the arachnides; as their organization is the most different 

 from that of the arachnides that v\c observe in any animals of this 



We cannot deny that in a task so difficult as that of which we 

 have given a sketch we have left many gaps to fill up. But we have. 



