1909.] OLFACTORY ORGAN OF TELEOSTEAN FISHES. 639 



In the Percesoces the olfactory organs show a wide range of 

 variation in the above examples of the different families observed. 

 In the Scombresocidge they are of a qviite peculiar and charac- 

 teristic form, unlike that seen in any other group of Teleostei. 

 In the Mugilidse a very distinct type occurs in which the olfactory 

 chamber is enlarged hj two accessory empty sacs, closely resem- 

 bling in form and position the accessoiy sacs found in the majority 

 of Acanthopterygii. In Ophiocephalv,s the general structure- of 

 the nose and the position of the single accessory sac in connection 

 with it bear a considerable resemblance to that of the Cyprino- 

 dontidae, differing however in the form of the rosette, which is of 

 a type found elsewhere only in certain Pleuronectids. In Sphyroina 

 there is yet another type of nose, with a large and very simple 

 accessory sac stretching forward like that of Merluccius or Zeus. 



Acanthopterygii. 



Pekciformes. 



Percid^, 



Perca fiuviatilis. 



The nostrils, which lie high up on the face slightly nearer the 

 eye than the snout, are both circular apertures of some little size 

 — the posterior Hush with the general surface, the anterior sur- 

 roimded by a low tubular lip. They are separated by a bridge of 

 skin about twice the diameter of the posterior nostril in breadth. 

 The olfactory chamber occupies the usual hollow^ in the ethmoid 

 and corresponds in length to the area between the nostrils. It is 

 occupied by a prominent oval rosette of some fifteen large laminae, 

 with strongly convex and swollen free margins. 



Above and below the rosette the nasal cavity is dilated to form 

 a pair of accessory empty sacs, the upper of which runs inwards 

 and forwards beneath the ethmo-maxillary ligament into the spaces 

 between the mesethmoid and the backward process of the pre- 

 maxilla and deep to the maxillary process of the palatine. The 

 lower dilatation extends in a similar way between the lachrymal 

 scute and the palate to the maxilla. Both these accessory sacs, 

 although in comparison with those of many other genera of 

 Acanthopterygii poorly developed and but indefinitely marked off 

 from the true olfactory chamber, evidently belong to the same 

 type and are in a similar way affected by movements of the pre- 

 maxilla and maxilla as the mouth is opened and closed, giving rise 

 to water currents in the olfactory chamber. 



Latrid^. 

 Latris ciliaris^. 



The olfactory organ closely resembles that of the Perch, although 



* This specimen was obtained through the kindness of Col. Nicholson. 



