338 



BIOLOGY: GENERAL AND MEDICAL 



weal formation, and intense itching. When these 

 mites are numerous the victim suffers consider- 

 able malaise and some elevation of the body 

 temperature. As the weals form, the bodies of 

 the mites become surrounded by the tumefied 

 skin and appear as minute transparent red 

 points at the centres. The life history of these 

 mites is not completely known. 

 The ticks and mites are not all parasitic upon 



FIG. 120. Leptus autumnalis. (After Trouessart.) 



warm-blooded animals; a few infest snakes, 

 reptiles, and even fishes. 



A peculiar arachnid, probably related to the 

 mites, the Liguatulid, is parasitic upon the 

 tongue of dogs. 



Phylum Chordata. Of the vertebrates there are very 

 few parasitic representatives. 



Class Pisces. The Hag-fishes may with pro- 

 priety be classed among the parasites. The 

 common hag, Myxine glutinosa, is an eel-like 

 fish, not infrequently 18 inches in length. 



