OYCLOSTOMATA. 355 



Sub-Class III— CYCLOSTOMATA. 



Skeleton cartilaginous, notochordal, the skull not separated from the 

 vertebral column ; is destitute of ribs, true jaws, or limbs. Mouth suctorial, 

 a single nasal opening. No bulbus arteriosus to heart. Six or seven gills on 

 either side in the form of fixed sacs, and destitute of branchial arches. Rays in 

 the vertical fins. Alimentary canal simple. No pyloric appendages, pancreas, 

 spleen, or air-bladder. Generative opening peritoneal. 



These cyclostornatous or circular-mouthed fishes are of a low type as evidenced 

 by the persistent notochord, absence of vertebral centra's, no trace of limbs and no 

 mandible, while their respiration is carried on in sacciform or lateral pouches, 

 and their mouths show their semi-parasitic habits. And although morpholo- 

 gists may consider their position is distinct from that of the true fishes, still here 

 they will still have to find a place in fish faunas. Kitchen-Parker (Nature, 1883, 

 p. 331) remai'ked that " the suctorial mouth has its highest development in 

 the lamprey ; in the Myxine and Bclellostoma there is no circular disk with horny 

 teeth, but merely an oval fissure surrounded by barbels, and having inside it 

 a huge tongue beset with two oblique rows of recurved and inturned horny teeth, 

 antagonized by a single ethnoidal tooth. In the larva of the lamprey the mouth 

 is not circular, and the lower lip is covered far back by the tipper which is like a 

 hood ; there are no teeth of any kind, only moss-like barbels or papillae under the 

 upper lip." When breathing, the branchial currents are independent of the 

 region concerned in deglutition. According to many observers, these fish would 

 appear usually to die after breeding. Panizza remarks that both male and female 

 lampreys after breeding are found dead. Benecke that the river lamprey 

 P. fluviatilis, after breeding, gradually declines and finally dies. The metamor- 

 phoses these fish undergo, require from four to five years. Lampreys were first 

 artificially propagated in Schleswig-Holstein, by Herr M. Frauen, May 24th, 

 1879, some hatched by June 3rd, and all by the 17th. 

 These fish are divisible into two families : — 



I. Petromyzontidce, the stone suckers or lampreys in which the single external 

 nasal opening terminates in a blind duct. 



II. Myxinidce or the hags wherein the nasal duct penetrates the palate. 



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