2826 THE BONY FISHES AND GANOIDS 



sac-gilled catfishes (Saccobranchus) , there is a long sac running down the muscles 

 of the back behind the proper gill chamber. Through this breathing sac blood is 

 carried from and returned directly to the heart; and in consequence of this arrange- 

 ment these fishes can remain alive for hours or even days apart from water, so that 

 they are able to traverse spaces where aquatic respiration is impracticable. Among 

 the Indian representatives of the family it is somewhat curious that whereas most 

 of the forms dwelling far in the interior of the country near and in the hills have 

 the air bladder ossified, this is not the case with those inhabiting the rivers of the 

 plains and the sea. The majority of the catfishes are inhabitants of the fresh waters 

 and estuaries of the tropical and subtropical regions of the globe; but, as we have 

 seen, one species is found in those of Eastern Europe, while a considerable number 

 enter the sea, although generally keeping near the coasts. They are found not only 

 in rivers, but likewise in lagoons and marshes. Day writes that ' ' they mostly prefer 

 muddy to clear water, and the more developed the barbels the more these fishes ap- 

 pear to be adapted for an inland or muddy fresh-water residence. The wider and 

 deeper the rivers, the more suited they are for the Siluridce, consequently the larger 

 forms are comparatively rare in the south of India, while they abound in the Indus, 

 Jumna, and Ganges, as also in the Irawadi and other Burmese rivers." It may be 

 added that they are equally common in the muddy waters of the La Plata river. 

 " Owing to their usual resort," continues the same writer, " these fishes appear to 

 employ their feelers in moving about in muddy places, and consequently have less 

 use for their eyes than forms that reside in clear pieces of water. This is one reason 

 why the size of the eye as compared with the length of the head is much greater in 

 the young than in the adult. The eye, in fact, atrophies, instead of increasing in 

 size in proportion with the remainder of the head. In some species the skin of the 

 head passes over the eye without any trace of a free orbital margin. In the genus 

 Arius, and some allied marine forms, the males appear to carry their ova in their 

 mouths, perhaps until the young are produced. Many of these fishes are credited 

 with causing poisonous wounds, and we frequently find such cases admitted into 

 hospitals. The injuries may be divided into two classes, namely, those in which 

 the wounds are of a distinctly venomous description, and those in which the jagged 

 spines occasion intense inflammation, often of a dangerous character." The flesh of 

 the catfishes is of an inferior quality, and generally eaten only by the lower classes. 

 All the members of the family are very tenacious of life, and extremely difficult to 

 kill. Geologically, catfishes date from the lower Eocene London Clay, where they 

 are represented by the extinct Bucklandium, apparently allied to an existing African 

 genus; while in the higher Eocene of the south of England there occur species re- 

 ferred to the existing genus Arius. An extinct genus has also been described from 

 the Eocene of North America; and in the Eocene of Sumatra, as well as in the Plio- 

 cene of India, the fossil forms belong to existing genera, and some of those from the 

 latter deposits even to species still inhabiting the same country. Numerically the 

 catfishes form an exceedingly large family, the existing types constituting consid- 

 erably over a hundred genera, many of which contain a multitude of species. In 

 this work only a very few of the genera can be even mentioned, some of those 

 selected including the largest members of the family. 



