386 . . ME, W. E. COLLLNGE ON THE [-A-pP* 2, 



It continues through the squamosal into the sphenotic and in the 

 region of pore number 7 divides into two branches, viz. the supra- 

 and sub-orbital. 



The Supra-orbital Branch passes through the sphenotic into the 

 frontal and makes a sharp turn to the region of pore number 9 

 (PI. XIX. fig. 6), and then in an outward curve passes around the 

 anterior nasal opening, where it tei'minates. 



The Sub-orbital Branch passes posterior and ventral to the orbit 

 in the sub-orbital bones, opening in its course b}' three pores. 



In the specimens I examined, the operculo-mandibular branch 

 differed from that figured and described by Pollard (11. p. 534) in 

 that there is a distinct mandibidar portion. It is not connected 

 with the main canal of the head, but arises near the head of the 

 preoperculum, through which it passes ; opening by three pores it 

 passes into the mandible, in which portion there is a single pore, 

 number 4 (PI. XIX. fig. 6). 



The species examined by Pollard was C. paleatus. If the con- 

 dition figured by this author is correct for the adult stages of 

 C. paleatus and Trichomyterus tenuis — he examined only young 

 forms of both — they are very interesting, and offer perhaps the 

 simplest type of sensory canals in the Physostomi. 



III. Cypkinid^. 



Labeo dussumieei. 



I do not propose to describe the sensory canal system in Labeo, 

 but wish to draw attention to the presence in this family of a series 

 of sense-organs which, so far as I can learn, are peculiar to it. 



Valenciennes ^ \^as the first, I believe, to make any mention of 

 them, and later Bleeker " pointed out their presence. Neither of 

 these authors described their structure, which was first detailed 

 and figiu'ed by Leydig (8) in the thorough and careful manner 

 characteristic of all this author's work ^. It is rather singular, but 

 I cannot find a single reference to this very important paper in 

 any of the writings of recent workers upon the subject. 



In Labeo there are distributed over the anterior region of the 

 head and around the borders of the mouth a large series of pores 

 of different sizes v^ith overlapping edges standing above the level 

 of the skin. These edges are quite smooth and unpigmented 

 (PI. XIX. fig. 7). 



Each pore leads into a flask-shaped cavity varying in size 

 according to the size of the pore (PI. XIX. fig. 8). The latter 

 average from 1 to 3 millim. in diameter in Labeo dussumieri, 

 the cavity being from 3 to 10 millim. in depth. Prom the 



'^ Cuvier et Valenciennes, Hist. Nat. des Poissons, 1842, vol. xvi. 



^ Bleeker, Atlas iohthyol. d. Indes-Orientales Neerlandaises, 1863, t. iii. 



^ The species described by Leydig are Schismatorhynchus hetcrorhynchus, 

 Blkr., Lobocheilus falcifcr, van Hass., and JRohita vittata, Val. Bleeker makes 

 mention of their presence in various species of the following genera : — 

 Crossocheilus, Labeo, Lobocheilus, Schismatorhynchus, Epalzeorhynchus, Bohita, 

 Diplocheilichtkys, Mondius, and Danzila. 



