7G4 PAEASITIC DISEASES. 



of growth of various species of gadfly. Tliese flies are generally 

 included in the genus CEstrus of entomologists, the CEstrtdce form- 

 ing a rather numerous family of the class Insecta, and belonging 

 to the order called Diptera. As the attention of the profes- 

 sion is often called to these singular creatures, it will be desirable 

 to give a brief account of their development and habits. 



There is yet another series of internal parasites, long ago 

 called Pentastomes, from the notion that they were furnished 

 with five mouths. These worms are also occasionally brought 

 under the notice of the practitioner of veterinary medicine; 

 and in one remarkable instance recorded by the late Professor 

 Dick, three of these entozoa caused the death of a valuable 

 sporting dog. These Pentastomes, in fact, are allied to the 

 true ticks, and therefore must be grouped along with all those 

 spider-like creatures, which, in common with the spiders them- 

 selves, breathe by means of peculiar air-vessels termed tracheae. 

 In other words, the Pentastomes belong to the order Trachearia, 

 forming a division of the class Arachnida. 



It thus appears that, without taking into consideration certain 

 minute parasitic organisms belonging to the lowermost class of 

 animals, and misnamed " cattle plague bodies," we have to deal 

 with no less than six well-marked orders of invertebrate animals, 

 one or more species of each of these orders being liable to play 

 the part of parasite within the body of some one or other of 

 our various domesticated animals. 



To such of the parasites as have an especial interest for the 

 profession, and which are included in one or other of the six orders, 

 namely, Nematoda, Trematoda, Cestoda, Acanthocephala, 

 Diptera, and Trachearia, the reader's attention is now invited. 



Classification of Entozoa. 



Sub-Kingdom Vermes (Worms). 



CI. I. Platyhelminthes (Flat-worms). 

 (K 0. 1.) Cestoda. 



(Fam. a.) Tceniadce (Tape-worms). 



Gen. Tcenia. 

 (Fam. h.) Boilwiocephalidce (Pit-headed worms). 

 Gen. Boihriocejplialas. 



