PREFACE. XI 



of the more common of our quadrupeds and birds have 

 been searched in vain. 



The opinion that each and every animal has its own pe- 

 culiar parasite, is not borne out by facts, for although in the 

 majority of cases a distinct species of insect is found upon 

 each particular animal, i. e. quadruped or bird, yet there 

 are several instances where the same kind infests three or 

 four different species of birds, but in such exceptions they 

 are almost always confined to individuals of the same genera 

 or family, or at least to species of similar habits. This is 

 more strictly the case with birds than quadrupeds. For 

 instance, Docophorus icteroides, I have found on nearly 

 every species of duck which has come under my notice. I 

 have received it from other birds also, but they were of 

 aquatic habits, and belonging to the order Natatores. The 

 Nirmus obscurus infests several species of Sandpipers, God- 

 wits, &c. The Nirmus rufus, upon several of the Hawks 

 and Falcons ; and Docophorus Lari upon nearly all the 

 Gulls. In the instances among quadrupeds, it is rather 

 doubtful whether the species is common to two different 

 animals or not, or whether they may not have been merely 

 transferred by associating or frequenting the same place of 

 abode ; as for example, the Trichodectes scalaris found 

 upon both the Ox and the Ass, where the animals are 

 feeding in the same stall, or sleep together, a transfer of 

 property might easily be made. The Hcematopinus Pili- 

 ferous infests Dogs, and I have received specimens from 

 the Ferret, which last animal was said to swarm with them. 

 Here it is rather difficult to account for the occurrence, as 

 I am not aware that the two animals ever live upon friendly 

 terms with each other; and moreover, the person from 

 whom I received them informed me he had not a dog. 

 When we extend our observations to genera, we find they 

 take a much wider range, and it is in only two or three 

 cases, that we could with any confidence assert that they 

 b 2 



