294 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDÆ. 
Fig. 2 . The same head as seen on the left or eyeless side. 
a a. Tubular scales of lateral line. 
72. Left supratemporal range of ossicles. 
73'. Left suborbital range, thus situated on the other side of the head from its eye, and ens the 
dorsal fin and both supratemporal ranges interpolated between. 
19. Left turbinal, or os terminale. 
Fig. 3. Sketch of the distribution of the mucus-canals on the right or ocular side of Platessa vulgaris, 
the Plaice. 
aaa. The main canal, extending from the tail along the lateral itis and along the head, between the 
eyes, till it ends on the inner or left side of the nostril, giving off on its way many little ducts, 
which open on the surface of the skin of the supratemporal branch, 6 5, which branch, though 
usually simple, is here bifurcated. 
ccc. Operculo-mandibular branch. 
dd. Right suborbital canal. 
e indicates the cross commissure given off to join the mucus-canal system of the opposite side. : It 
gives off a little duct to the skin at the posterior margin of the orbit, and then passes to the left 
side, beneath the cephalic end of the dorsal fin. 
Fig. 4. The same head, seen from the eyeless side. 
aa a a. The main canal as before, but stopping short at the cross commissure ü Ye 
b. Supratemporal canal, not so long as in the right side. 
ee c. Operculo-mandibular canal. 
d d d. Left suborbital canal, stillremaining on this side, while its eye has been transferred to the right side. 
a’, A small follicle or detached portion of mucus-canal, the representative of the nasal extremity of the 
main canal of this side, the portion intervening between it and the cross commissure having 
disappeared. (See also Plate XXXII. fig. 3, where this arrangement is represented diagram- 
matically.) 
e. Cross commissure. 
E. Upper eye, a small pottion of which is, in the Plaice, visible from the left side. 
Fig. 5. Sketch of the distribution of the mucus-canals on the right or ocular side of the head of Platessa 
pola. The same letters refer to the same canals as in the head of the Plaice, fig. 3. The 
commissural (e), however, ends blindly : thus there is in this fish no connexion eene the 
canal-systems of the two sides. 
Fig. 6. The left side of the head of the same fish, the mucus-canals being here seen to be dilated into 
large ampullze, which communicate with each other by smallopenings. Each ampulla generally 
sends only one little duct to the external surface of the skin. 
aa a a a a. The lateral canal and the series of six ampullæ on the main canal of the head. : 
a’. The part detached from the rest, and lodged in the left turbinal. It is the homologue of the little 
follicle marked a’ in the Plaice, fig.'4. 
bo bb. The four ampullæ into which the supratemporal canal is dilated. 
cccc. The eight ampullæ of the operculo-mandibular branch. 
d d d d. The six ampullæ of the suborbital branch. 
Fig. 7. Skeleton of the left side of the head in Platessa pola, showing the bones supporting the ampul- 
lated mucus-canals. 
50. Suprascapular. 
+72. The five supratemporal bones. 
73'. The five suborbitals. 
19. Turbinal ossicle, or os terminale. 
34. Præoperculum ; and 
