CAT-FISHES. 



113 



cobranchus (363) there is a long air-sac^not the air-bladder, 

 which is also present, enclosed in a bony envelope — but a thin- 

 walled sac extending from the first gill-slit on each side along the 

 body as far back as the tail, and this allows the fish to exist out 



Fig. 55. — Accessory respiratory organ of Clarias as seen after the removal 

 of the gill-cover; a and/» the two accessory organs, ba l -ba* the gills. 

 (After Bridge, Camb. Nat. Hist., vii, 1904.) 



of water for several days. The aerated blood from these air-sacs 

 is carried back into the general circulation by means of the efferent 

 vessels of the last gills, which join the aorta ; the blood is not 

 taken back straight to the heart. Most Siluroids can live in foul 

 water even though not provided with accessory organs of respir- 

 ation ; they rise to the surface and take in air through their 

 mouth. 



The Wels, Sihirus glanis, 364, is a fish occurring plentifully in 

 the Danube and other fresh waters of continental Europe, but 

 absent from France, Spain and Italy. It is said to grow to a 

 length of ten feet and a weight of three or four hundred pounds. 

 The male watches over the eggs and defends them from marauders, 

 a fact which was noted by Aristotle. In the North American 

 Bull-heads (Amhirus, 373) also the male guards the eggs, and 

 defends the young after they are hatched. Arius (376) and 

 Galeichthys (377), guard the eggs by carrying them in the 

 capacious mouth, the male, more rarely the female, being the 



i 



Wels. 



