Ewing — Significance of Parasitism in Acarina. 69 



cestor which was very similar to our present day cheese mites, a 

 member of which is represented by Fig. 12.— Fig. 12. Rhizoglyphus 

 pJiylloxerae Riley, dorsal view. A good representative of the family 

 Tyroplyphidae "Cheese Mites." This species is found in this country 

 upon old decaying grain, etc. — Fig. 13. Sarcoptes scabiei De Geer, 

 male from below. This is the itch mite of man. In the assumption 

 of a small round form of body, of long stout spines on the legs, and 

 the rudimentary mouth-parts, it has adapted itself to a life within the 

 skin of man. — Fig. 14. Demodex folUculorum Simon, ventral view. 

 This species is taken from the hair follicles of man. Several closely 

 related forms are found in similar situations in other animals. Ap- 

 parently it has little resemblance to the itch mite of Fig. 13, yet we 

 have very strong evidence that the two are closely related. The ex- 

 treme reduction of the legs and mouth-parts, and the very long drawn 

 out, wormlike body are all beautiful adaptations for the life in hair 

 follicles. — Fig. 15 and 16. Megninia magna Ewing, male and female 

 respectively as seen from below. This species, as well as the other 

 members of the Analgesidae has adapted itself to a life among the 

 feathers of birds. Scarcely any degeneration is noticed, but on the 

 contrary it shows a higber state of evolution than the ancestral type 

 in the development of very efficient partial-vacuum suckers on the 

 tarsi, and in the marked sexual dimorphism shown. Phylogenetically 

 this species is closely related to the two preceding. 



Plate v. — Special Adaptations. — Fig. 17. SyringopMlus elongatus 

 Ewing. The very elongate form of body, found In this and a few other 

 allied species, is a curious adaptation for living in the quills of bird's 

 feathers. The affinity of this species with the Cheyletidae, a family the 

 free-living members of which are highly evolved forms, appears to be 

 established. — Fig. 18. A Hydrachnid larva. These larval parasites 

 of the Hydrachnidae, show the palpi modified into adhering organs, 

 being provided with stout claws and working horizontally. In some 

 species, as in this one, the presence of long hairs on the legs show 

 an adaptation for locomotion in the water. — Fig. 19. LaMdocarpus 

 compressus Ewing. The members of this genus exhibit a remarkable 

 adaptation in the form of the anterior group of legs, which do not 

 look at all like legs and which as locomotor organs are useless. These 

 legs have become reduced to a single segment which is much flat- 

 tened, strongly curved, and strongly chitinized. The two pairs 

 oppose each other and when contracted strongly grip a single hair to 

 which the parasite is attached. — Fig. 20. A Hydrachnid larva. The 

 last segment of the palpus has been transformed into a strong hook 

 by means of which the mite clings tenaciously to its host. The 

 species is chiefly a wader, as is shown by the absence of long hairs 

 on the legs, in this respect it has not become perfectly adapted to 

 the aquatic life. — Fig. 21. A dipterous insect with a larva of Rhyn- 

 cholophus attached. Shows the exposed position assumed by 

 many of these parasitic larvae and the great necessity of having good 

 adhering organs. 



