MYVXINE, 519 
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 palzeo- 
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- 4 Barbules; m., mouth opening. 
out the usual pancreas. The ¢2, first eill-pouch cat open 
anus lies within an integumentary {fshowjpterna) lamella se #.% 
cloacal chamber. canal of first gill-pouch ; ts 
Respiratory system.— Water {tosinon calen geen 
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 
