56 Trans. Acad. Sci. of St. Louis. 



follicles of man and other mammals. Here evidently 

 the form of body best adapted is that which these mites 

 have assumed, the vermiform type (PI. IV, Fig. 14). 

 Perhaps the most beautiful adaptation of this vermiform 

 body is shown in those mites which inhabit the quills of 

 bird's feathers. We find it well illustrated in the genera 

 Picohia and Syringophilus which have this habit (See 

 PL V, Fig. 17). 



As is true of most external parasites specialization in 

 the form of clinging or clasping organs may become 

 highly developed. Besides the claws or hooks, which have 

 been mentioned, we have several other structures of con- 

 siderable interest. In the Analgesidae there are devel- 

 oped upon tarsal pedicels partial- vacuum suckers (See 

 PI. IV, Figs. 15 and 16), which are very effective as 

 adhering organs. These forms when placed on a smooth 

 glass surface adhere so tightly that it is very hard to 

 lift them off with a sable-hair brush. 



The well known development of the hypostoma in the 

 ticks is also a good example of specialization. Here the 

 hypostoma becomes greatly developed into the form of 

 a dart and is provided with many strong recurved teeth. 

 When this structure is thrust into the skin of the host the 

 recurved teeth act like the barbs on a fish-hook against 

 its being withdrawn. 



The most varied and interesting cases of specializa- 

 tion in the form of clinging organs are found in the Vil- 

 licolata. In the family Listrophoridae we have several 

 genera .represented, all of which have some specialized 

 apparatus developed for clasping hairs. 



In the case of the genus Listrophorus the underlip is 

 modified into a large, curved, flexible plate, which can 

 be brought around a hair so as to clasp it very effect- 

 ively. In the genus Lahidocarpus the front two pairs 

 of legs have been entirely changed from their primitive 

 shape, and each consists of a single, strongly curved chit- 

 inous plate entirely without appendages (See PI. V, Fig. 

 19). These appendages when opposed to each other 



