MYXINE. 



may be, as in the lamprey, a combination of olfactory and 

 pituitary involutions. The absence of pigment and sensory 

 structures in the skin, and the simple . state of the eye and 

 ear, may be partly associated with the hag's mode of life. 

 It seems probable that the simplicity is primitive rather 

 than degenerate. 



Alimentary system. The 

 mouth is suctorial. There is a 

 median tooth above, and two rows 

 of teeth are borne on each side of 

 the muscular "tongue." These 

 teeth are entirely "horny," but 

 sharp. Into the mouth, just in 

 front of a fringed velum which 

 separates it from the pharynx, the 

 nasal, or, as some would say, the 

 naso-pituitary, sac opens. Thus 

 water passes from the nostril into 

 the pharynx. It may be, as Beard 

 suggests, that this passage is a per- 

 sistent "old mouth," the palaeo- 

 stoma of Kupffer. From the gullet 

 open six respiratory pouches, each 

 of which has an efferent tube, and 

 the six efferent tubes of each side 

 unite in a common exhalant ori- 

 fice. The gut is straight and FIG. 274. Respiratory sys- 

 uniform, with wavy longitudinal tem of hag, from ventral 

 ridges internally, with a two-lobed surface. 

 liver and a gall-bladder, but with- *-,Barbuies; *.., mouth opening 



__, on ventral surface ; g.. gullet ; 



out the usual pancreas. The 



li^c wifhin art inform m^nfarv 



itegumenrary 



Chamber. 



Respiratory system. Water 

 may enter by the nasal sac or 

 by the mouth. It passes into the pharynx, down the 

 gullet, into the six pairs of respiratory pouches and 

 their efferent tubes, and leaves the body by the single 

 aperture at each side. The respiratory pouches have 

 much-plaited internal walls, on which the blood vessels are 

 spread out. On the left side, behind the sixth pouch, a 



.. 



., first gin-pouch, cut open 



to show internal lamellae ; ^-.JJ.6, 



sixth gm _ pouch . ex ^ exfifinJ 



canal of first gill-pouch; &., 



^common e 



