598 ORGANS OF SECRETION. 



Notwithstanding the scaly covering of fishes, their exte- 

 rior surface is generally lubricated by a copious viscid mucous 

 secretion poured out on different parts of the body, from long, 

 ramified, subcutaneous, muciparous glands. These simple 

 glands are especially distinct and numerous on the head and 

 sides of cartilaginous fishes, where they form long tortuous 

 tubes filled with their white mucous secretion. In many of 

 the osseous fishes they form a continuous tube extending 

 along each side of the body to the end of the nose, and 

 sending down branches along the operculum and the lower 

 jaw. These muciparous vessels, like other secerning tubuli, 

 secrete at all points of their course, and pour out their secre- 

 tion on the surface from distance to distance as they proceed 

 below the skin, and they are often seen following the course 

 of the longitudinal lateral line on both sides of the body. 



Besides the ordinary secretions of the pulmonary, the 

 urinary, and the generative apparatus, many fishes both of 

 fresh water and of the sea, and both osseous and cartilagi- 

 nous, are provided with complicated electrical organs, pre- 

 senting an immense secreting surface in small space, and by 

 which they are able to communicate violent shocks to ani- 

 mals which touch or approach them. In the gymnotus 

 these organs consist of an upper larger and a lower smaller 

 pair, and occupy the inferior part of the whole caudal region 

 of the body. They are divided by numerous closely approxi- 

 mated transverse membranous folds, and these horizontal 

 compartments are further subdivided by innumerable thin 

 vertical laminee like the plates of a galvanic pile, with a 

 mucous secretion interposed between the layers, and filling 

 all the cells thus formed, and they are largely supplied with 

 nerves, as are all the electrical organs of fishes. The 

 two distinct electrical organs disposed along each side 

 of the body, are separated from each other by firm ten- 

 dinous membranes and by muscles, and they extend ta- 

 pering to the end of the tail. The membranous septa are 

 highly vascular to furnish their abundant secretion, and they 

 are supplied with symmetrical pairs of spinal nerves derived 

 from the whole course of the spinal chord. In the torpedo 

 the electrical organs occupy a large space on each side of the 

 head ; they are composed of numerous small vertical com- 

 partments, each of which is regularly subdivided by a series 

 of horizontal parallel septa or thin membranous lamina^ 



