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SUB-PHYLUM CRANIATA. 



DIVISION MARSIPOBRANCHII OR CYCLOSTOMATA- 

 (ROUND MOUTHS.) 



State briefly the principal features of the Lamprey (Petro- 

 myzori) and the Hag -fish (Myxine). 



(The general characters of the Cyclostomata are in bold type.) 



LAMPREY (Peiromyzori). 



Body eel-like. 



Skin, smooth and scaleless, secretes 

 muCUS. A pigmented skin with 

 sensory structures. 



Without paired fins. Two dorsal 

 unpaired fins, and a caudal fin 

 around the tail. 



A round suctorial mouth, without 

 jaws. The mouth has a prominent 

 sucker-like buccal funnel with 

 numerous horny teeth and with 

 papillae on lip. Behind the mouth 

 there is a ventral toothed " ton- 

 gue " ; it has horny teeth, and 

 is worked like a piston. 



Paired gill-pOUChes. Seven pairs 

 (with gill lamellae) on walls of 

 a sub-pharyngeal tube, which is 

 blind posteriorly, but which opens 

 anteriorly into the pharynx. The 

 gill-pouches open separately to 

 the exterior. 



A velum between buccal cavity and 

 sub-pharyngeal tube. 



Endostyle of pharynx becomes 

 thyroid gland (in adult). 



Intestine has a slight spiral valve. 

 Anus opens into a cloaca. 



Liver is without gall-bladder and 

 bile-ducts (in adult). 



HAG-FISH (Myxine). 



Body, eel-like. 



Skin, smooth and scaleless, secretes 

 much mucus. 



A median fin around the tail. 



The rounded lipless mouth has 

 sensory barbules. Two rasp-like 

 rows of horny teeth on " tongue," 

 and a median palatal tooth. 



Six pairs of gill-pouches on walls of 

 pharynx. A tube from each pouch , 

 and the tubes of each side uniting 

 to form one ; the pouches there- 

 fore opening collectively to ex- 

 terior by one common aperture 

 on each side. 



A velum between buccal cavity and 

 pharynx. 



Intestine is without a spiral valve 

 Anus opens into a cloaca. 



Liver (bilobed) with associated 

 gall-bladder and bile- ducts. 



