Animal Dentition 259 
parasitic in habit, and furnished with sucking ~~~7~~~~—~~_. 
cylindrical mouths in place of jaws. In these ! oy 
so-called fishes there are no true calcified teeth, . Ne 
the place of which is taken by horny structures 
serving the same use. The general character PRE 
of the dentition of the common lamprey will 
be apparent from the accompanying illustration 
(Fig. 15), and it will accordingly suffice to say 
that the teeth of the lips are arranged in con- 
verging rows, which may be as many as twenty 
in number, with four or more in each row. In 
addition to these, are a few larger teeth situated 
near the centre of the mouth which vary in form 
and arrangement in the different groups. In a o 
Chilian species, for example, there are two tri- oO 
angular groups of three teeth each on the upper & 
side of the mouth, opposed by two pairs of double Fig. 14. Upper Dentition of a Lung-Fish (Ctenodus) 
teeth below. Tuame of the Coal Period. 
preys prey on other fishes, to the sides of which they 
adhere by means of their sucking mouths while they rasp 
away the living flesh of their victims with their cruel 
teeth. On the other hand, the hag-fishes, in which the 
arrangement of the teeth is somewhat different, generally 
infest the interior of their involuntary hosts, among which 
the cod is frequently selected for their unwelcome atten- 
tions. When these fishes first attach themselves to their 
prey, the single curved tooth in the middle of the palate 
is thrust into the flesh to serve as a holdfast, after which 
the work of destruction is carried on by the laterally- 
opposed saws formed by the other teeth, aided by the 
sucking action of the mouth. 
In the next and final article of this series it is pro- 
posed to discuss the teeth of the modern bony fishes and 
Fig. i5. Dentition of Lamprey. their extinct enamel-scaled relatives. 
| ad > s 
SSS 
" 
