196 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



Mange- or Itch- Mites exhibit degrees in parasitism. Some 

 of them (Dermatophagus] simply devour the loose scales which 

 are constantly being detached from the epidermis, while others 

 (Dermatocoptes) suck blood. But the most objectionable (Sar- 



coptes, fig. 1142), those respon- 

 sible for the unpleasant disease 

 known as " itch ", actually bur- 

 row in the skin, within which the 

 female lays her eggs, and may 

 therefore be described as true 

 internal parasites. They live on 

 the blood and other juices of 

 their hosts. 



A curious little elongated mite 

 (Simonea folliculorum, fig. 1142) 

 lives in the little bag-like glands 

 attached to the roots of hair, in 

 Fig. i, 42 . -A, Root of hair; (*) enlarged, showing a which a sort of fatty matter is 



swollen sebaceous gland (b}, containing a Hair-Mite Qprrptprl 

 (Simonea folliculoruni}. B, A Hair-Mite, greatly en- 

 larged, c, An Itch-Mite Sarcoptes scabei}, greatly The degenerate TonP"Ue - 



Worms ( Linguatulida ), which 



live in the noses 01 dogs and wolves, are doubtfully classed with 

 the Arachnida (see vol. i, p. 393). 



CRUSTACEANS (CRUSTACEA) AS PARASITES 



A large number of the lower Crustaceans are parasitic, and 

 some of them have become extremely de- 

 generate as the result of their mode of life, 

 especially in the case of the females. A 

 few examples must suffice. 



FORK - FOOTED CRUSTACEA (COPEPODA) 

 AS PARASITES. Many of the members of 

 this group are found attached to fishes, 

 usually by means of their suctorial mouths. 

 They are popularly, though somewhat in- 

 appropriately, known as Fish - " Lice ". 

 Among the least modified kinds are those 

 (Argulus, fig. 1143) found attached to the 

 skins of carp and sticklebacks, holding on by a couple of suckers 



Fig. 1143. A Carp-" Louse' 

 (Argulus), enlarged 



