122 



ANIMAL PHYSIOLOGY. 



[LESSON 34. 



impulse by the contractions of these organs, and, after having been 

 oxygenized, it is returned, partly by vessels of the skin, but chiefly 

 by a direct and continuous lateral vessel (k, k), to the dorsal artery (g). 

 This artery extends from one end of the body to the other. At 

 its middle part it receives many transverse branches from the diges- 

 tive tube, and through them joins the inferior intestinal vein (7^;. 

 The vascular network thus formed around the intestine gives origin 

 to two veins at the sides (i), which terminate in the dorsal vessel, 

 immediately behind the ventricles (f, d). 



LESSON XXXIY. 



ORGANS OF NUTRITION IN THE EPIZOA. 



FIG. 204. 



Actheres percarum, female. 



564. The Epizoa (epi, upon ; zoon, 

 an animal) form a most extraordinary 

 class of animals. They are external 

 parasites, usually on the bodies of 

 Fishes, where they attach themselves 

 to the skin, the eyes, and the gills. 

 Their number is prodigious, probably 

 exceeding that of the fishes they infest. 



Limited space will not allow of 

 more than one illustration of this 

 class the Adheres percarum found 

 attached to the eye of the Perch. 



565. The mode by which the Ler- 

 naea (as these animals were called by 

 Linnseus) adhere to their prey, is pe- 

 culiar, and characteristic of the class. 

 A pair of hollow, tubular feet, ad- 

 hering by their terminal extremities 

 (Fig. 204, Z, Z), gives origin to a cup- 

 shaped sucker (m) ; this is the instru- 

 ment of adhesion. 



566. The mouth consists of upper 

 (b) and under jaws, the latter pro- 

 vided with feelers ; besides these, a 

 pair of jointed antennae, each termi- 

 nated by three small bristles (a). 

 The alimentary cacal is, as in all 



