BY J. DOUGLAS OGILBY. 393 



Up to the present time but little has been definitely proven with 

 regard to the degree of relationship which exists between the 

 Marsipobranchiates on the one hand and the more recently and 

 highly developed Teleostomes on the othei', but the preponderance 

 of evidence tends to show that the former are the survivors of a 

 very primitive type of the Chordates, the oldest living represen- 

 tatives of which are to be found amoiig the HeptatrematidcB. 



The Marsipobranchil are divisible into two Orders, which may 

 be briefly characterised as follows : — - 



Nasal duct tube-like, penetrating the palate; mouth without 

 lips; eyes wanting; snout with barbels 



Hyperotreti* 



Xasal duct a blind sac, not penetrating the palate; lips and 

 eyes present; no barbels 



HyperoartiiI 

 - The first of these Orders contains two Families, the Heptatre- 

 matitlce and the Myxinidce, the members of which are variously 

 known as Hag-Fishes or Borers; they are small, colourless, more 

 or less parasitic, marine animals, living at a moderate depth, and 

 wholly carnivorous. In places where they are common they do 

 no inconsiderable damage to the fishermen by destroying the 

 hooked fishes, into whose body they burrow and upon whose 

 tissues they feed internally. They inhabit nearly all the seas of 

 temperate regions, and three genera, PoIistotrema,l IIeptatrema,\\ 

 and Myxine § have been differentiated. 



* imepoia, palate; rprjios, perforated. 



t inepcaa, palate; aprios, entire. 



X PoUMofrema, Gill, Proc. U.S. Nat. AIus. ISSl, p. 30. Type, Gastro- 

 branchii'i dombey, Lacepfede. ttoXih, many; laros, vertical; TprjjjLa, a per- 

 foration; in allusion to the increased number of external gill-openings. 



II Heptatrema, Dumeril, ? Diss. Poiss. Cyclost. Type, Petromyzon 

 cirrhatus (Forster), Bloch & Schneider. enTa, seven; rprjua, a perforation; 

 -Bdellostoma, Miiller, Abh. Ak. Wien, 1834, p. 79 (1836). 



§ Myxine, Linnaeus, Syst. Nat. i. 1758. Type, Myxine glutinosa, 

 Linnaeus, pv^lvos, a slimy fish, from pv^a, slime; so named on account of 

 the excessive amount of slime secreted by the mucous sacs of these animals, 

 which is so great that the exudation from a single living example is 

 sutScient to gelatinise a pailful of water. 

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