1909.] olfactory organ op teleostean fishes. 643 



Sparid^. 

 Pagellus centronotus. 



The olfactory organ is comparable to that of the Perciformes 

 previously described, particularly to that of Midlus, but is in 

 every way better developed. 



The nostrils have a similar position and form, differing only in 

 the fact that they are relatively closer together and that the 

 posterior is protected from ingress by a special valvular fold (text- 

 fig. 209, C, p. 644) attached to the inner surface of its posterior lip. 



The olfactory chamber is almost completely filled by a very 

 prominent oval rosette of the normal type, in which the individual 

 laminae have a sharply convex free margin. The cavity is not 

 prolonged between the hinder margin of the rosette and the 

 posterior nostril, but above and below the ridge that carries the 

 olfactory nerve to the rosette are a pair of clearly defined oval 

 apertures that lead into ethmoid and lachrymal sacs of a similar 

 character to those of Midhcs or other Perciformes, but larger and 

 more markedly diflferentiated from the true olfactory chamber by 

 the narrowness of their channels of communication. The position 

 of the olfactory chamber and accessory sacs with regard to the 

 bones of the skull is similar to that previously described, the 

 lachrymal sac lying beneath the lachrymal bone upon the palatine 

 and the buccal membrane and reaching forward to the strongly 

 convex posterior border of the maxilla, and the ethmoid sac 

 occupying the usual position between the ethmoid and the back- 

 ward process of the premaxilla. From their position both sacs, 

 and especially the lachrymal, must be strongly compressed during 

 the closure of the mouth. 



_- Sitmmary. 



The olfactory organ shows a strong general resemblance in all 

 the members of the Perciformes examined, accompanied by an 

 interesting series of variations tending towards more perfect 

 specialization. 



The nostrils occupy in all a very similar position, rather high 

 up on the face not far in front of the upper border of the eye. 

 In the simpler forms {Perca, Latris, Gaj^ros, and Beryx) they 

 are both widely open, in Mullus and Pagellus the posterior is 

 valved. In all the olfactory chamber is dilated beyond the actual 

 olfactory area, the dilatation showing a gradual difierentiation 

 into two clearly defined accessory sacs, one related to the ethmoidal 

 region in such a way as to be compressed and expanded by the 

 movements of the premaxilla, the other lying upon the palatine 

 bone and the buccal membrane, and responding in a similar way 

 to the movements of the maxilla or {Cajyros) mandible. 



Within the group a line can be drawn between Perca, Latris, 

 Capros, and Beryx on the one hand, where the accessory sacs, 

 although differing in size, are still but little cut off from the 

 olfactory chamber, and in which the posterior nostril is not valved, 



44* 



