. The elasmobranch fishes. Chondrichthyes. 280 THE ELASMOBRANCH FISHES groups {isa. and mpo.). In addition to these there is a modified ampulla in the spiraeular wall. In active forms the pores to these organs may be very numerous as in Mvstelus cams in which practically 1600 have been counted. In a sluggish type like Torpedo there are as few as 162 (Norris, 1929). Each ampullar}^ organ (fig. 246) consists of three parts: (1) a pore or opening to the exterior (op.); (2) a canal or tubule {th.); and (3) the ampulla proper (a.), located in the in- . - tegument. The ampulla varies as to pattern i
. The elasmobranch fishes. Chondrichthyes. 280 THE ELASMOBRANCH FISHES groups {isa. and mpo.). In addition to these there is a modified ampulla in the spiraeular wall. In active forms the pores to these organs may be very numerous as in Mvstelus cams in which practically 1600 have been counted. In a sluggish type like Torpedo there are as few as 162 (Norris, 1929). Each ampullar}^ organ (fig. 246) consists of three parts: (1) a pore or opening to the exterior (op.); (2) a canal or tubule {th.); and (3) the ampulla proper (a.), located in the in- . - tegument. The ampulla varies as to pattern in the different Elasmobranchs. In some it is not divided up into ampullary pockets. In others it may have from eight to twelve pockets. These pockets are usually con- nected by a single canal with the outside pore. In Hexan- clius, however, Dotterweich (1932) has recently shown that each ampullary pocket in a group has its ovn\ canal and that a group of canals empties by a common pore. A trans- verse section through the am- pulla (fig. 247a) shows how they and the partitions sepa- rating them are cut. Accord- ing to Peabody (1897) each ampullary pocket ipl'.) has a double lining, the inner layer of which is of cells of large size. The pockets are surrounded by connective tissue and maj^ themselves surround a central part, the ampullary centrum {en.). Figure 247b is a sagittal section through the centrum. The section is through a pocket on the left and a partition between two pockets on the right. In figure 248 it is seen that the nerve to the ampulla enters through the centrum and spreads out over the ampullary pockets. It was formerly supposed that the cap over the centrum was the sensory area in which the nerve terminated, but in figure 248 it appears that, while the nerves lose their medullary sheaths and only the axis cylinders run toward the central cap, the fibers turn outward as the fibrils surround the ampullary sacs. Dotterweich (1932) has recently shown that the wall
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