OF THE ANNULOSA. S8i 



labours of Lister, Homberg, Clerck, Degeer, Olivier, W'al- 

 kenaer, and Latreille. On entering this class we find ani- 

 mals still parasitical and still hexapod, even when the type 

 of the Acaridea, as well as of the other Arachnide orders, 

 is undoubtedly octapod. In the genus Siro we are led by an 

 easy transition from the Mites to the Phalangidea, hence 

 by Galeodes to the Scorpionidea and Araneidea. From 

 these last we may possibly be able to return to the Acaridea 

 by means of genera like Trombidiofi. This is a series of affi- 

 nities, all of which, excepting the last, have been noticed 

 by the modern French entomologists; so that for the pre- 

 sent I shall refer to their works for the proofs requisite to 

 substantiate the accuracy of the progression. As to the 

 manner in which the series is here divided, it must on the 

 other hand be considered as barely an approximation to 

 the truth; so that, having thus chalked out a mere outline 

 of the distribution of the Arachnida, I may be permitted 

 hereafter to correct it in proportion as its inaccuracies 

 shall be detected. It may, however, with more confidence 

 be stated that the Arachnida are connected with the Crus- 

 tacea, by means of the Pyciwgonida, because the observa- 

 tion and the consent of all the first entomologists of the 

 present day unite in confirming this affinity. 



The Arachnida difter from Crustacea in having their 

 respiratory organs always internal, and opening on the sides 

 of the abdomen and thorax to receive the air. These la- 

 teral apertures are common to them with Insects, and are 

 known to physiologists by the appellation of Stigmata. 

 When these stigmata communicate with pulmonary 

 pouches, there is a circulation effected by means of a dor- 

 sal and muscular heart, from which two great vessels pro- 



