and smooth or simple Byes of Insects. 289 



ihvertebral animals, and these inquiries have proved that the clo- 

 portce, which I had placed among the insects, belonged to the 

 cla«;s of arachnoidcs; and tl]at plmlangia, which I had pre- 

 sumed to have the same organization with the spiders, ought to 

 be classed with the insects, since they present trachea and a 

 dorsal vessel without vascular ramifications. As to the cluporUe, 

 they have a true heart provided v%ith vessels, the blood of which 

 goes to receive the impression of the air, into particular organs 

 not ramified, and which we may consider as species of lungs. 

 With respect to the organs of circulation and respiration, the 

 cloporice are nearer the scorpions than the spiders. In fact, 

 the latter have a heart very much enlarged at its base : al- 

 though this heart extends afterwards to the extremity of the 

 bodv, it by this enlargement resembles that of the cnistaceons 

 (hcapodes, with this difference, however, that the position of 

 tiiese two organs is not the same. Tlie heart of the crustacece 

 is situated in the breast, while that of spiders is in the abdomen 

 and the side of the back. y\s to the heart of scorpions, we do not 

 see that it has any very sensible enlargements ; in this respect 

 this organ more resembles the heart of the doportce than that 

 of the spiders. But it is truly worthy of remark, that the or- 

 gans of respiration are multiplied in proportion as the heart takes 

 an uniform diameter. Thus in the si)ider, in which the heart 

 is decidedly swollen, there exist only two lungs : in the cloportcs 

 the heart, without showing any sensible enlargement, as in the 

 spider, nevertheless presents a diameter a little more consider- 

 able towards its upper part : thus we observe they have four 

 hmgs : finally, in the scorpions this number amounts to eight ; 

 but the heart in all these animals is of a diameter nearly uniform 

 throughout its whole extent. To conclude : in all the arach- 

 noides the lungs are always symmetrical, and are never found but 

 in pairs. It is possible' that the form of body may also have 

 sdme influence on tliat of the organs of respiration, and parti- 

 cularly of circulation. Thus the greatest diameter of the heart 

 in certain species of spiders would supply what was wanting in 

 length. Nevertheless, this cause ought not alone to have in- 

 fluence, since in all the spider race the heart extends from one 

 extremity of the body to another. The heart of the spiders 

 begins, in fact, at the bottom of the abdomen; but as it sends 

 two princi])al vessels into the breast, we may say that it extends 

 from one extremity of the body to the other. 



As to the nervous svstem of the true spiders, it is always com- 

 posed of a cerebriform ganglion, situated in the upper part of 

 the body, wliicii we may eitJier call head or breast, because it 

 performs functions analogous to those two parts. This ganglion^ 

 situated almve the oesophagus, surrounds it most frequently 

 Vol. -14. No. 19S. Oil. IHII. T by 



