FISHES. 317 



eggs. By means of their circular mouths, horny teeth, 

 and sucking tongues, the lampreys attach themselves to 

 fishes, from which they suck the mucus and frequently 

 the blood. In some places the large sea-lampreys are 

 regarded as delicacies, but usually they are not esteemed 

 as food. 



SERIES II. GXATHOSTOMATA. 



This group, the name of which means jaw-mouth, 

 includes the great majority of vertebrates in which true 

 jaws, capable of closure, occur. The skeleton, sometimes 

 of cartilage, sometimes of bone, is a true support to the 

 body; usually paired limbs are present, and there are a 

 pair of nostrils. The preceding general account of the 

 Vertebrata (pp. 290 to 315) applies especially to the 

 gnathos tomes. The group is subdivided into Ichthyop- 

 sida, Sauropsida, and Mammalia. 



GRADE I. ICHTHYOPSIDA (FISH-LIKE FORMS). 



Under this name are grouped fishes and batrachians, 

 since they are alike in certain important respects. Thus 

 they have, either as larvae or adults, functional gills, they 

 have lateral-line organs, they have median fins, and the 

 blood is cold. Besides these there are several other points 

 of union, notably in the development, especially promi- 

 nent being the absence of two embryonic structures, the 

 amnion and allantois, which occur in higher forms. The 

 Ichthyopsida are divided into two classes: Pisces and 

 Amphibia. 



CLASS I. PISCES (FISHES). 



The forms to which the name Fishes is usually applied 

 have a body adapted in shape and structure for an aquatic 

 life. It is usually covered with scales, which lie between 



