548 MR. H. M. KYLE OK NASAL 



an adaptation to semi-sedentary, as opposed to migratory, habits 

 of life. 



The function of these sacs in the first stage is moreover aptly 

 described, as has been said, by the word " reservoir." In the 

 tolerably quiet life these animals lead, the water containing 

 odoriferous particles will not pass so freely over the olfactory 

 epithelium as in the case of the free-swimming migratory forms. 

 These sacs are, however, distended and constricted by the 

 movements of the premaxillae and maxillae, and are thus able 

 to draw in water, the odoriferous particles in this way coining 

 into contact with the sensory epithelium without necessitating 

 any movement on the part of the animal as a whole. 



The second stage, where definite secretory sacs are present, 

 has been found so far only in the family of the Heterosomata 

 comprising the Halibut, Plaice, and Turbot groups. The secre- 

 tion is forced from the sacs into the nasal cavity and over the 

 sensory epitheliiim by the movements of the premaxillge and 

 maxillae, in a fashion similar to the water in the previously 

 described species. 



The function of these secretory sacs is not very evident. They 

 are absent in other Teleostei so far as is known, and this might 

 mean that the olfactory organ is of little importance or that 

 the epithelium is maintained sufficiently sensitive by water 

 alone. In the air-breathing Vertebrates the nasal secretion is of 

 importance in cleansing the organ, in keeping the sensory 

 epithelium in a healthy sensitive condition, and in aiding towards 

 bringing odoriferous materials into a state of solution favourable 

 to their full appreciation. "When the secretion is present in 

 Pishes, therefore, it may signify that the olfactory organ is much 

 used and of great importance. Such, indeed, would seem to 

 be the case with the flat-fishes mentioned. In the life these 

 animals lead as ground-feeders, searching for their food almost 

 entirely by sense of smell, this secretion may be of as much 

 service in cleansing the olfactory epithelium and maintaining it 

 sensitive as the nasal secretion of the air-breathing Vertebrates. 



In the Sole group the secretory has given place for the most 

 part to a water-retaining function. This change might at first 

 sight appear strange, as a return to a previous condition, although 

 the animals are more sand-loving in their habits than even the 

 Plaice, Halibut, and Turbot, and in most cases have their 

 olfactory organs as largely developed as these forms. But the 



