388 ON THE ORDERS 



pair, until this also disappears about the confines of thia 

 group and Winged insects. In this manner M . Latreille's 

 doctrine becomes an argument for proving the Crustacea 

 to be naturally interposed between the Arachnida and Pa- 

 rasitical insects, which indeed are only connected by that 

 property which the opposite points of a group always pos- 

 sess of approaching to each other. 



The true Arachnida have no lateral antennae, but only 

 a pair answering to the intermediate pair of these organs 

 in Crustacea, and which in the former animals is always 

 connected with manducation. Their head is always in 

 some degree confounded with the thorax ; the stigmata 

 occupy only a part of the body, and even in those species 

 which breathe by means of tracheae communicate with a 

 simple tracheal cord, which, from its ramifications, may 

 almost be termed radiated. The Parasitical insects, on 

 the other hand, have no intermediate antennae, but only a 

 pair which represents the lateral pair in Crustacea, and 

 which in these animals is never used for purposes of man- 

 ducation. The head is always distinct from the body; 

 and the stigmata, which are disposed over almost the whole 

 length of each side, communicate with a bifurcated tra- 

 cheal system. 



Having now described, as briefly as I conveniently 

 could, the natural connexion of those orders into which 

 the Aunulosaa re resolvable, it may not be improper to 

 give a summary view of the affinities as they may be ex- 

 pressed by a table. In this table, however, the distribu- 

 tion of the Crustacea and Arachnida is presented to the 

 reader with much diffidence of its accuracy, and that 

 chiefly on the following account. 



If we establish a chain of organic gradation solely upon 



