590 TELEOSTEI chap. 



poisonous property of the dermal secretion of the Fish. Cope 

 believed au orifice at or above the axil of the pectoral fin in 

 Notnras to be the opening of the duct of a poison-gland; "from 

 it may frequently be drawn a solid gelatinous style ending in a 

 tripod, each limb of which is dichotomously divided into short 

 branches of regular length." I think this condition of things 

 has notlring to do with a poison-organ, and is merely a repetition 

 of what is observed in Loaches and in the Characinid Xeno- 

 charax, where I have found a gelatinous substance filling the 

 short duct by which the membrane of the air-bladder is placed 

 in communication with the skin and the sensory organ of the 

 lateral line, ilost Silurids can live in very foul water, taking in 

 air from the surface, and spend a comparatively long time out of 

 the water, without being possessed of any special apparatus for 

 atmospheric respiration. A few genera, however, are provided 



Fig. 356. — Harinout, Clarias anguillaris (after Valenciennes). \ nat. size. 



with an accessory breathing organ : in Clarias, Heterohranchus, and 

 allies, there is a dendritic superbranchial organ, in Saccobra7ichus 

 a long air-sac, extending from the first branchial cleft along the 

 side of the body, as described above, p. 295 ; and these Fish can 

 live for days on land. Clarias lasera has been observed, in Sene- 

 gambia, to spend several months of the dry season in burrows, 

 from which it emerges at night to crawl about in search of food. 

 Many Silurids, but especially Doras and Synodontis, are known 

 to produce sounds in and out of the water by means of a special 

 mechanism of the air-bladder and the processes of the vertebrae 

 above it, combined with the movements of the pectoral spine 

 grinding in the glenoid cavity.^ In South America, Doras has been 

 observed to move rapidly on land, projecting itself forward on the 

 pectoral spines by the elastic spring of the tail, travelling long 

 journeys over land, from one drying pond to another, spending 

 whole nights on the way ; these migrations sometimes take place 



1 Cf. Sorensen, C. R. Ac. Sci. Ixxxviii. 1879, p. 1042, and " Lydorgane hos Fiske '' 

 (Copenhagen, 1884) ; Bridge and Haddon, P.R.S. Iv. 1894, p. 439. 



