HIGH SCHOOL ZOOLOGY. 



81 



No adult fish has external gills of this character, although the embryos 

 of various Elasmobranchs have, and Protopterus has three filamentous 

 gills attached to the pectoral arch. 



Perhai)S the greatest external difference is in the form of the 

 paired limbs, which no longer resemble the unpaired fin as they 

 do in fishes, but are jointed into the same divisions as they are 

 in the higher Vertebrates, and divided at the ends into fingers 

 and toes, of which there are four to each limb in the Menobranch. 

 But these limbs are not able to support the weight of the body ; 

 the chief organ of locomotion is still the taU, and that is flatten- 

 ed and provided with an unpaired fin as in the fishes. It is 

 however not furnished with any skeletal support such as the 

 lin-rays of the fish. 



2. At first sight the skin 

 of the Menobranch is very 

 like that of the catfish, but 

 care will be required to 

 make out the system of 

 sensory canals in the head 

 and along the lateral line, 

 and no traces of bony scales 

 will be found in the skin. 



Microscopically the most im- 

 portant difference is in the pre- 

 sence of numerous cutaneous 

 glands which furnish the 

 abundant mucus which lubri- 

 cates the skin. 



3. Important differences 

 will be detected in the 

 skeleton, but more in the 

 skull than in the vertebral 

 column. In the latter the 

 individual vertelirse are am- 



phiccelous, and bear short ribs in the trunk region which do not 

 encircle the body cavity. There are no interspmous bones. 



Fig. 59.— Skull of Menobranch, from above. 

 (After Huxley.) 



Pnix, prenia.xilla ; vo, vomer ; pi, palatine ; 

 s^i, s<iuaniosal ; pro, prootic; st, stapes ; epo, 

 cpiotic ; Tr, frontal ; ant, antorbital cartilage; 

 q, (juadrate ; pa, parietal ; e, e.xoccipital. 



Cartilage dotted ; cartilage-bones heavily, 

 membrane-bones lightly shaded. 



