116 



ZOOLOGY 



SECT. 



1. EXAMPLE OF THE CLASS.- -THE LAMPREY (Petromyzon). 



Three species of Lamprey are common in the Northern Hemi- 

 sphere : the Sea-lamprey (P. marinus), which attains a length of a 

 metre : the Lampern, or common fresh-water Lamprey (P. fluvin- 

 tilis), about 60 cm. in length : and the Sand-pride, or lesser- 

 fresh-water Lamprey (P. Iranchialis), not exceeding 30 cm. in 

 length. In the Southern Hemisphere the Lampreys belong to two 

 genera : Mordacia, found on the coasts of Chili and Tasmania, and 

 Gfeotria, in the rivers of Chili, Australia, and Xew Zealand. Both 

 genera differ from Petromyzon in minor details only. 



External characters.- -The head and trunk (Fig. 749) are 

 nearly cylindrical, the tail-region compressed or flattened from? 



FIG. 749. Petromyzon marinus. Ventral (A), lateral (B), and dorsal (C) views of the head.. 

 /'/. cl. 1, first gill-cleft ; ina:. f. buccal funnel : ."'.". : , eye ; //<f/<. mouth ; na. ap. nasal aperture ;. 

 /'. papillae; pn. pineal area; t l . t-. t%. teeth of buccal funnel; ? 4 . teeth of tongue. (After 

 W. K. Parker.) 



side to side. At the anterior end, and directed downwards, is a 

 large basin-like depression, the luccal funnel (buc.f.), surrounded 

 with papillae (p.) and beset internally with yellow, horny teeth 

 (t l t 3 ). At the bottom of the funnel projects the end of the 

 tongue (t*), also bearing teeth, and having immediately above it 

 the narrow mouth (mtli). On the dorsal surface of the head is the 

 single median nostril (na. ap.), and immediately behind it a trans- 

 parent area of skin (pn.) indicates the position of the pineal organ. 

 The paired eyes have no eyelids, but are covered by a transparent 

 area of skin. The gill-slits (br. d. 1) are seven pairs of small aper- 

 tures on the sides of the head, the first a little behind the eyes. 

 On the ventral surface, marking the junction between trunk and 



