1G4 SUPPLEMENT TO THE ORDERS 



ter to relax, and give passage to the urine. Farriers used to 

 employ the same remedy with horses in similar cases. 



The pediculi proper, are confined to men and quadrupeds. 

 The ricini, or bird-lice, to the feathered race. 



It appears that the ancients designated under the name of 

 ricinus, those acarides, or acari, vulgarly called ticks, which 

 attach themselves to the skin of dogs, oxen, &c. Degeer 

 might, therefore, have better employed another denomination 

 for the present genus, and which preceding naturalists con- 

 founded with that of lice. Accordingly, Dr. Leach has 

 adopted, from Herman, the denomination of nirmiis. 



It was by no means surprising, that the earlier naturalists 

 did not distinguish these animals from the lice ; their exter- 

 nal physiognomy is almost the same, but their organization, 

 as appears from the text, is different in many essential points. 

 We shall not repeat that description here, but merely remark 

 that it is evident from it, that these two genera approximate 

 in a natural series. From the consideration of their resem- 

 blances and differences, and from some other facts, furnished 

 by the trachean arachnida, and the branchiopoda, M^e may 

 see that nature, in preserving always the same type of general 

 forms, is pleased to modify, and sometimes rather abruptly, 

 that of the manducatory apparatus, or that she easily con- 

 verts organs adapted for grinding, into sucking organs, and 

 vice versa. Her views in this respect are subordinate 

 to the model on which the body of the animal is at first 

 formed. This consideration caused M. Latreille to reject, as 

 a primary character, the division of insects into two lines — 

 one composed of the grinding, and the other of the sucking 

 insects. 



The ricini live exclusively on animals of the class Aves. 

 Degeer, it is true, makes mention of a ricinus found on the 

 body of a dog; but this species M. Latreille refers to pedi- 

 culus, and could discover no mandibles on it. 



