148 Papers frmn the Department of Marine Biology. 



The organs of Astroscopus form two irregular, vertical columns, one 

 just behind and somewhat under each eye, the muscles of which are 

 embedded in the organ. Each organ is roughly oval in section and is 

 composed of a number of parallel plates separated by electric connec- 

 tive tissue and made up of about 20 separate electroplaxes lying side by 

 side. The number of plates in each organ does not exceed 200, but 

 they are very thin and their constituent electroplaxes are deeply 

 indented on the edges. The electroplax bends on itself so as to over- 

 lap on its own body at some points of considerable area, and so as to 

 make it necessary for the overlapping portion to find room in the next 

 layer in which to secure nerve and blood supply. From 3 to 5 of 

 the larger electroplaxes form the central area of the layer and from 

 8 to 12 smaller ones are arranged around it and fill in the outhne. 

 The electroplax is placed in the organ with the electric layer upward 

 and the nerve supply approaching it from above. The blood supply 

 comes into contact with it on the lower or nutritive surface, which is 

 evaginated into a number of papillae that occupy more than two-thirds 

 of the thickness of the electroplax. The nuclei of these papillae are 

 oval and differ slightly both in size and shape from those of the electric 

 layer, which are evenly arranged in a series. The striation of this layer 

 is remarkable and quite as definite and conspicuous as in the weakest 

 of the Rajidae (plate vi, fig. 3). It consists of fine, sharp lines spaced 

 evenly and parallel to one another, but curved in many directions. In 

 section one appears to be looking on various surfaces, the striations 

 on one surface being parallel to each other but crossing above and below 

 other sets of similar parallel striations. Dahlgren believes these lines 

 to represent the edges of an equal number of curved and parallel sur- 

 faces, seen in actual or optical section. There is no variation in the 

 distance between the hues, however, and no oblique or surface views of 

 the striations appear (Dahlgren 36). 



The nutritive layer is composed of two parts, one of wliich includes 

 the nutritive nuclei, the evaginations, and the heaviest area of the 

 striations. In the other layer there are no nuclei, but the striations 

 continue and can be traced even into the thin electric layer, which con- 

 tains a row of evenly spaced nuclei and the peculiar rods described by 

 Dahlgren and in further detail by J. G. Hughes, of Professor Dahl- 

 gren' s laboratory (62). 



The nerve supply of Astroscopus consists of a number of medullated 

 fibers that run between the layers in the electric tissue and end at all 

 points on the electrical surface. The origin of the nerve supply, as well 

 as the origin of the electric organs themselves, could not be surmised by 

 Dahlgren and Silvester (36) at this time, owing to the complications in 

 the adult. The muscles and nerves of the eye pass directly through 

 the organs and the nerve which supplies the electric tissue is in some 

 way curiously involved with the oculomotor nerve, but no connection 



