SECRETORY SACS IN TELEOSTEI. 5-1-7 



function, from secretory to water-retaining, being accompanied 

 by changes in the tissues, may have led to a great change in 

 structure, and that Natural Selection has been thereby confronted 

 by variations which it will convert into specific differences. Or, 

 discarding Natural Selection and questions of "advantage" 

 and " survival of the fittest," it seems simpler and more natural 

 to believe that the remaining longer than usual with the head 

 buried in the sand, *'. e. a slight change in habit*, may have 

 brought about the perforation of the roof of the mouth, in 

 which case the presence of the naso-pharyngeal communication, 

 accompanied by the change of habit and habitat, would have a 

 " discriminative " as distinguished from a " selective " value. 



Whichever way the matter be argued, we see how this im- 

 portant " modification " gives us the possibility of a new species, 

 although it is better perhaps to wait for additional evidence 

 before recording it as such in the classification of the Hetero- 

 Bomata. 



The discovery of a naso-pharyngeal communication in only one 

 specimen so far does not, however, lessen the interest attachino- 

 to its presence. Such facts are rare in the class Pisces, so that, 

 when they do occur, their general importance is so great as to 

 render the question of their specific value a somewhat secondary 

 matter. The importance and interest do not lie in the uniqueness 

 of this single individual, but in the occurrence in the Teleostei of 

 on organ hitherto unknown in them and considered as almost 

 peculiar to the air-breathing Vertebrates. 



We may now turn our attention to more general consider- 

 ations, and in the first place to those of function. The first 

 stage, or most elementary condition, where " reservoirs " with 

 water-retaining function are present among Fishes, is found in 

 Lahrus, Scorpoena, Gastrosteus, and AnarrhicTias, but it is absent 

 in the Gadidse so far as examined, as also in the Herring. These 

 sacs are also absent from the Sail-fluke, a highly specialized 

 Heterosomid, which lacks the " recessus orbitalis "f and has 

 departed from the sand-loving habits of the other flat-fish. These 

 facts lead to the conclusion that the presence of nasal " sacs " is 



* In another species of the Sole-group, it was found that certain parasites 

 ( Lerncsa ?) had made their way into the nasal sacs and had caused a perforation 

 of the roof of the mouth ! 



^ Cf. Holt, E. W. L. : " Studies in Teleostean Morphology." Proc. Zool. 

 Soc. 1894, p. 422. 



