130 



EPIZOA. 



detached. In the second example, (c, d,) besides the rudimentary 

 limbs, the lower surface of the head and ventral aspect of the body 

 (d) are covered with sharp spines calculated to increase very 

 materially the tenacity of its hold upon the surface from which it 

 imbibes food. The sacculi appended to the posterior part of 

 the animal are receptacles for the eggs, and will be explained 

 hereafter. 



These examples, however, are taken from the most imperfectly 

 organized Epizoa ; but, as we ascend to more highly developed 

 species, we shall at once see how gradually an approximation is 

 made to the articulated outward skeleton, and jointed limbs, met 

 with in the homogangliate forms of being, until at last the zoolo- 

 gist remains in doubt whether the more elaborately constructed 

 ought not to be admitted among the crustacean families, which 

 they most resemble. 



(170.) The Adheres percarum (fig. 53) is one of those spe- 

 cies most nearly allied to the ARTICULATA ; and, the details of its 

 anatomy having been fully investigated by Nordmann,* it will 

 serve as a good example of the type of structure which prevails 

 throughout the class. 



The Actheres is found to infest the perch (Percafluviatilis), 

 adhering firmly to the roof of the mouth, to the tongue or some- 



Fig. 53. 



times even to the eyes of that fish ; 

 in which situations it is concealed by 

 a brownish slimy secretion, so that 

 its presence might easily escape the 

 notice of a casual observer. 



The female, which is represent- 

 ed in the figure, is about two lines 

 in length; the male, which differs 

 materially from the other sex in many 

 points, is considerably smaller. 



The outer covering of the body of 

 these little creatures is at once seen to 

 have assumed a horny hardness ap- 

 proximating the density of the cover- 

 ings of the articulated classes, and in- 

 dications are even perceptible of a 

 division into segments : the distinct- 

 tion, moreover, between the trunk 

 (cephalo-thorax), to which the limbs 



* Mikrogvaphische Beitriige zur Naturgeschichte der witbellosen Thiere ; Berlin, 1832. 



