JULY 121 



the activity of the salivary glands, which secret a 

 viscid fluid used in the architecture of their nests. In 

 the common swift it binds the particles of earth into a 

 firm concrete; but swifts of the genus Cobacalia use 

 little other material than their own saliva. Man, being 

 indeed omnivorous, has discovered that the nests may 

 be dissolved into a palatable stock for soup, highly 

 esteemed by Chinese epicures; but Western gastro- 

 nomy has not yet been educated to regard the saliva 

 of any animal as a delicacy ! 



It seems grimly appropriate that swallows, martins, 

 and swifts, which subsist by preying upon flies, should 

 in turn be afflicted by a winged parasite peculiar to 

 themselves. This is a dipterous fly of the family 

 Hippoboscidcc, named Stenopterix kirundinis, whereof 

 two or three generally lurk in the plumage of each 

 bird. This fly, which is closely related to the sheep- 

 tick (Melophagus ovina), the forest fly (Hippobosca 

 equina), which torments thin-coated horses so intoler- 

 ably, and the parasite of the red deer (Lipoptena cervi), 

 has such a hard, horny skin that the swallow cannot 

 rid its nest by devouring the creature. Knowledge of 

 these parasites is still very imperfect; it is believed, 

 however, that, luckily for the birds infested by them, 

 they are not bloodsuckers, but content themselves by 

 feeding on the scurf at the roots of the feathers. Still, 

 one cannot but think that the presence of these loath- 

 some, clinging vermin, each of which bears about the 

 same proportion in bulk to its host as a full-grown rat 

 does to a man, cannot be otherwise than grievously 

 irritating. 



