TEXT-BOOK OF ZOOLOGY 



M.. 



n. 



L. 



the suckers of a cuttle-fish). The suctorial mouth, however, is of far 

 more important use in the acquisition of food 

 than for locomotive purposes. By means of 

 horny teeth, the lamprey rasps the skin of fishes, 

 and then sucks in the parts it has scraped 

 off, as well as the blood and other body juices. 

 It also consumes carrion in a similar manner. 

 The water required for respiratory purposes can, of 

 course, not be taken in by the mouth when this is 

 attached by suction. It is conveyed to the gills, 

 which are contained in pouches, by seven apertures 

 visible behind the eyes, and is discharged again by 

 the same openings. The animal thus carries on 

 its head nine apertures, viz., the seven branchial 

 openings just mentioned, a single eye, and a 

 median unpaired olfactory pit (nose) : hence in Ger- 

 many the fish is known as "nine-eyes" (Neunauge}. 

 The skeleton is cartilaginous, and the vertebral 

 column has the form of an unsegmented rod, which 

 is described as the notochord. 



The Sea- Lamprey (Petromyzon marinus) almost 

 completely resembles the fresh-water lamprey in 

 structure and mode of life. This species reaches 

 a length of little more than 3 feet. 



ORDER V.: LANCELETS (LEPTO- 

 CARDII). 



SKELETON consisting only of an unsegmented sup- 

 porting rod (notochord) ; no skull or heart. 



The Lancelet (Amphioxus lanceolatus}. 



(Length up to 2J inches.) 



This singular little fish is found buried in the 

 sand along the seashore. It represents not only 

 the lowest member of the class of fishes, but also 

 occupies the lowest stage in the vertebrate division of 

 the animal kingdom. The body of this animal is 

 colourless and almost transparent, pointed in front 

 and behind, and provided with a membranous fin- 

 like border (F) at the caudal end. The skeleton is represented merely 



THE LANCELET. 

 (x 2 diameters.) 

 E. , Eggs ; L., Liver ; Mu. , 

 Muscle-segments. The 

 remaining letters are 

 explained in the text. 



