SEOEETOET SACS IN TELEOSTEI. 543 



there are two, in the Sole tribe only one, in the aberrant Sail- 

 fluke {Lepidorhombus whiff) none at all. lu the Halibut, Plaice, 

 and Turbot tribes, when the sacs are developed they lie anterior 

 to the ethmoid, and are closc4y connected with the pterygo- 

 palatine and maxillary bones (PI. 38. fig. 1, n.s.-^-ii.s.^. In the 

 genus Solea that of the right or eyed side also lies anterior to the 

 ethmoid, whilst that of the left or blind side extends posteriorly 

 over the roof of the mouth to as far back as the posterior third 

 of the parasphenoid (fig. 2, l.n.s.). In the above-mentioned 

 groups the function of these sacs is entirely secretory, their 

 blind ends resting on a layer of fatty tissue immediately over 

 the integument lining the roof of the mouth (fig. 1, f't.). In 

 the genus Solea the larger, posteriorly directed sac acts for the . 

 most part as a reservoir just as in the cases cited. A small 

 quantity of mucus is certainly always found in it, but mixed with 

 a large percentage of sea-water. 



In order to render fully clear the significance of these facts, it 

 is necessary to state the correlated diff'erences in form and struc- 

 ture of the several species of flat-fishes. This would lead too far 

 away, however, from the subject at present in hand, and it need 

 only be said that the Soles are better adapted for more sand- 

 loving habits than are the Halibut, Plaice, and Turbot. 



Leaving the physiological significance of these sacs for dis- 

 cussion later, we may turn now to a remarkable form first de- 

 scribed by Dr. Giinther *, a native of the China Seas, and called 

 by him Cynoglossus semilcevis. This species is included under a 

 sub-family of the Sole group, but is well marked ofi" from the 

 true Soles, and is probably of separate origin. In European 

 waters it has a near ally in the small Ammopleurops {Plagusia 

 of the French ichthyologists) of the Mediterranean. The charac- 

 teristics of the true Soles — the curved snout projecting in front of 

 the mouth, the small eyes and largely developed olfactory organs, 

 the slender and slightly developed opercular bones with contours 

 completely hidden by the skin, the comparatively small branchial 

 openings, and various other internal peculiarities of skull and 

 skeletoa — are accentuated in Cynoglossus, and indicate a greater 

 adaption to sand-loving habits than is found even among the 

 true Soles. The degeneration of the fins evidenced in these 

 latter reaches its extreme. The pectoral fins have entirely 



* Ann. & Mag. Nat. Hist. ser. 4, xii. 1873, p. 379, and ser. 7, i. 1898, p. 261. 



