384 ON THE ORDERS 



in Crustacea, exercise a function so secondary, that after 

 gradually becoming modified in those genera, such as 

 CyamuSf which come near to the Arachnida, and after 

 almost even disappearing, as in the genus Phyllosoma, 

 they may be considered as being altogether null in the 

 Araignees palpistes of Lamarck. Nevertheless my readers, 

 whom I suppose all to be entomologists, need scarcely to 

 be informed that the last mentioned animals possess organs 

 which are commonly termed mandibles, organs which 

 Linnaeus,- in the Spider, named " ungues sen retinacula" 

 and which in the Scorpion he regarded as " Palpi che- 

 Itfformes." Now, it will be asked What organs among 

 the Crustacea do these two mandibles, ungues, or che- 

 liform palpi of the Arachnida represent ? Savigny was 

 of opinion that they took the place of the second pair of 

 pedipalpi ; but Latreille answers the question in quite a 

 different manner. He refers to the changes which the two 

 intermediate antenna? of the Branchiopoda undergo, and 

 finds a resemblance even between these organs in the 

 brachyurous decapod Crustacea, and the mandibles of 

 Phalangium. He further observes that these organs in 

 both the tribes,' — that is, the internal antennas of Crustacea 

 and the mandibles of Arachnida, — have a similar situation, 

 namely, above the labrum and entrance of the oesopha- 

 gus, together with a similar mode of insertion, being pa- 

 rallel at their base, and only taking an oblique or curved 

 direction at their extremities; — whereas, on the other 

 hand, all true pedipalpi are situated below the labrum, 

 and are inserted immediately above the breast. 



M. Latreille then adopts the remark of Lister, that all 

 Annulose animals have a distinct head, and that the head 

 of Spiders and Scorpions is that part of the thorax which 



