202 FOURTH BKPORT 1834. 



or more segments of the thorax with the head. The class thus 

 characterized, which, according to a new nomenclature of his 

 own*, he calls Aranistes, he divides into the two subclasses of 

 Acarulistes and Armmlistes ; the former containing the single 

 order Acariens ; the latter the three orders of Phalangiens, 

 Ar aniens, and Scorjnoniens. Each of these orders is again 

 divided into several families. 



The rest of Dug^s's memoir is restricted to the investigation 

 of the Acari, and contains some novel and highly important re- 

 searches on this group of animals. These relate more espe- 

 cially to the gradual development of the young, and the meta- 

 morphoses which many of them undergo before arriving at the 

 adult state. M. Duges has satisfactorily ascertained that many 

 of the hexapod genera constituting Latreille's family of Micro- 

 phthira are only the larvfe of others, and he has sufficiently 

 multiplied his observations to lead him to suspect that this will 

 be found ultimately to be the case with all of them ; that is to 

 say, that there will be found no instance of any of the Arachnida 

 having only six feet in the adult state. He has proved Leptiis 

 to be only the young of Trombidium, and he has strong reasons 

 for supposing Ocypete and Astoma to be so likewise. The genus 

 Achlysia of Audouinf he has shown to be the larva of Hy- 

 drachna : the genus Caris he suspects to be the larva of Argas. 

 Although these striking researches necessarily lead to the sup- 

 pression of many genera instituted by former naturalists, Duges 

 has discovered or established others more than sufficient to make 

 compensation. In his arrangement of these animals we still 

 find twenty-four genera, distributed under seven families, the 

 former exceeding by five the number adopted by Latreille. It 

 is his intention to treat of each of these genera separately. As 

 yet, however, his valuable memoir remains unfinished. 



But few individuals besides Duges have hitherto devoted much 

 of their attention to the Acari. In 1826, Heyden published a 

 systematic arrangement of this grouplj:, in which he increased 



the want of antennfe. Latreille, however, was led subsequently to take a dif- 

 ferent view of the subject, and to regard what are usually called the mandibles 

 or chejiform palpi in the Arachnida as representing the intermediate pair of an- 

 tennae in the Crustacea Decapoda, only in the former class exercising a different 

 function and being always adapted for manducation. Thus the deficient parts he 

 considered to be the true mandibles, and not the antennae. See jFVijw. Nat., p. 307. 

 See also some remarks on this hypothesis of Latreille, by MacLeay {Hot. Ent., 

 p. 383,) and likewise by Duges {I. c, p. 9.). 



• In this and some other instances Duges has very unnecessarily changed 

 names which had long been consecrated by time, and adopted generally. 



t Mem. de laSoc. d'Hist. Nat. de Paris, torn. i. p. .98. 



t his, 1826, p. 608. 



