S9'2 ON THE ORDERS 



Arachnida ; convinced, as I am, that it is my duty to 

 warn the inexperienced reader of the circumstance before 

 he enters on the study of the following columns. 



1. 2. 3. 4. 5. 



Haustellata. Mandibulata*. Ametabola. Crustacea. Arachnida. 



1. Diptera Hymenoptera Vermes Branchiopoda Acandea 



2. Aptera Coleoptera Annplura Decapoda Araneidea 



3. Hemiptera Orthoptera Thysanura Ampbipoda Scorpionidea 



4. Homoptera Neuroptera Chilopoda I.aemodipoda Phalangidea 



5. Lepidoptera Trichoptera Chilognatha Isopoda Sironidea ? 



Of these five columns I consider the three first to be 

 distributed not very inaccurately, and to deserve much 

 more confidence than the fourth and fifth. Unfortunately, 

 from not having studied the affinities of these last with the 

 care required by analysis, I have been unable to detect 

 the principle upon which their analogies are graduated. 

 There are naturalists, 1 well know, who will object to 

 the supposition that these are graduated on any other 

 scale than that which we are certain of, such as the exter- 

 nal appearance. But as, independently of their form, the 

 analogical characters of the groups of Mandibulata and 

 Haustellata are founded on the variation of metamor- 

 phosis ; so there is reason to believe that some principle 

 of analogy, unconnected with their general appearance, 

 may hereafter be found to exist between every other two 

 contiguous columns. Sure enough it is, that, with re- 

 spect to external form, these analogies are remarkably 

 conspicuous, and as usual have been mistaken for affini- 

 ties. Thus it was that Linnaeus, Miiller, and others, came 

 to confound the Calygi with true Epizoaria; and that 

 Latreille says of his Branchiopoda, " Plusieurs de ces ani- 

 maux sont de veritables suceurs, et se rapprochent a cet egard 

 des Arachnides" such as the Acarida for instance. Nay, 

 if this train of reflection on the nature of relations of ana- 



