PARASITES. 



578 ] 



PARASITES. 



eluded a number of microscopic animals 

 and plants infesting other animals and 

 plants, and often nourished at the expense 

 of their structures or juices. Almost every 

 animal and plant is subject to parasites, 

 both in the young and the adult state ; and 

 in some instances, the parasites are them- 

 selves infested by other parasites. The 

 parasite may live on the surface of the 

 parasitiphore or host, or within its tissues 

 and in the cavities of its organs ; hence the 

 division of parasitic animals into epizoa 

 and entozoa. The commonest parasites 

 either feed upon the decaying external 

 skin -tissues, or are nourished at the expense 

 of the blood and fluids. In some remark- 

 able instances, as in the cirripeds, the male 

 appears to live parasitically upon the fe- 

 male; and in almost every case of para- 

 sitism there is a complicated life-cycle, often 

 accompanied by strange adaptations and 

 degenerations of form, so that often the j 

 parasite ultimately resembles but slightly its j 

 free and primitive form. Of the Animal 

 Parasites, many are not microscopic, but 

 the following sketch may be useful for 

 reference. The chief portion belong to : 

 The CRUSTACEA, Order Siphonostoma, as 

 Caligus, Cecrops, Lcemaryus, Nicothoe. The j 

 ABACHNIDA, Ord. Acarina, as Sarcoptes, 

 the itch-insect j the Ixodea, or ticks ; the 

 Gauiasea, on insects ; Trombidium, the 

 harvest-bug; the Hypoderidee, in birds; 

 the Phytoptidse, in galls. The Insects, 

 especially the Anoplura, as Hcematopinus, 

 Pediculus (the louse), and Phthirius ; Pedi- 

 cinus', and Trichodectes. The ENTOZOA, 

 as Tcenia (Ccenurus, Cysticercus, Echino- 

 coccus) ; Distoma, in the liver; BiUiarzia, 

 in the human blood-vessels, the ova in the 

 urine in endemic hsematuria and chyluria ; 

 the Nematodes, Anyuillula infest, and ster- 

 coralis, and Dochmius, in tropical diarrhoea ; 

 Sclerostoma syngamus in poultry, producing 

 the " ga^es ;" Strongylus pergracilis in the 

 Grouse-disease. The Infusoria, Opalina, 

 Trichomonas, &c. ; and the GBEGABINIDA, 

 Psorospermia in mammals, and insects 

 (PEBBINE). 



These are described under the respective 

 heads. 



The Plants parasitic on animals chiefly 

 belong to the class of FUNGI, and are tole- 

 rably numerous ; but many of the forms 

 which have been described are certainly 

 not distinct plants. They will be most con- 

 veniently enumerated under the heads of 

 the classes of animals infested. 



Man and Mammalia. 

 On the Skin. ACHOBION Schoenleinii and 

 PUCCINIA favus, on the hair and in the 

 follicles, in favus. TBICHOPHYTON ton- 

 surans, on the hair in plica polonica and 

 favus; this appears to be a TVww/a-like 

 growth, probably not a mature plant. TV.? 

 sporuloides, Rob., occurs in plica ; and Tr.? 

 ulcerina, Rob., in the pus of ulcers. Micro- 

 sporon Audouinii occurs in the hair-fol- 

 liclos in porrigo decalvans ; M. mentayro- 

 phytes. on the beard &c. ; M. furfur, on the 

 skin of the chest &c. in pityriasis versicolor. 

 The occurrence of Mucor mucedo on the 

 skin, and of an Asperyillus in the external 

 conduit of the ear, must be regarded us 

 accidental. 



On the mucous surfaces or in cavities. 

 SABCINA ventriculi in the stomach ; Tomla 

 cerevisice (?), ditto. Various species of 

 LEPTOMITUS, which must be regarded as 

 imperfect mycelial growths, found in almost 

 all the cavities of the body. Oidium albi- 

 cans, the fungus of aphtha, probably a pe- 

 culiar condition of PENICILLIUM ; Lcj)/<>- 

 tlirix buccalis, a filamentous growth constant 

 between the teeth, probably some allied 

 mycelium. 



Birds. 



Various species of ASPERGILLUS have 

 been found in the lungs and air-sacs ; their 

 introduction would appear to be accidental. 

 In the eggs of the common fowl, DACTY- 

 LIUM oogenum occurs not unfrequeutly, 

 sometimes on the membrane of the yolk, 

 sometimes on the outer membrane/ just 

 beneath the shell. SPOBOTBICHUM brun- 

 neum, Schenk, in the white of eggs, convert- 

 ing it into a brownish gelatinous mass. 



Reptiles and Fishes. 



On the skin of Tritons, as of Fishes, 

 ACHLYA (Saproleynia) is frequently ex- 

 tremely developed ; other obscure forms are 

 also enumerated by Robin. The same author 

 describes the PSOBOSPEBMI^E as Algse allied 

 to the Diatomaceae ; but they are pseudo- 

 naviculae of GBEGABINA. 



Berkeley has recorded the occurrence in 

 Denbighshire, on the scales of goldfish, of a 

 lichen identical with one which is found on 

 stones in neighbouring streams. 



Insects 



are subject to the invasion of various para- 

 sitic fungi, among the most remarkable of 



