The nutritive layer is composed of two parts, one of which 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 between the electric tissue and the eye-muscle tissue is evident, although the rectus inferior muscle has become so narrow as to appear as a mere thread and the rectus superior muscle is split into several parts by the passage of the electric nerve through it. The organ is bounded by the upper part of the muscle adductor mandibuhe, the muscle levator arcus palatini, and the anterior and posterior divisions of the muscle adductor arcus palatini.
The authors supposed the organs to have been derived from one of the bounding muscles, probably the muscle levator arcus palatini, since this has a more intimate connection with the organ than either of the other two, but the possibility was suggested of the tissue having arisen from the eye-muscles which pass through the organ. It was impos sible to follow up either of these theories, however, without embryonic material, and a search for embryos was at once begun.
Opsanus and Porichthys lay their eggs in nests or easily available places. This did not prove true of Astroscopus, how ever, and Professor Dahlgren studied the habits of the fish to find if possible where to look for the young forms. He found
the habits of Astroscopus to be essentially similar to those of an allied form, Urano scopus scaber, a native of the Bay of Naples. This fish, as explained by Dr. Cerruti (so), lays a pelagic egg which at once floats from the bottom, where it is deposited, to the surface, where it rapidly forms an embryo that lives on the surface for many weeks and months. Astroscopus has a large pelagic egg which is laid in May or June and develops into a larva very rapidly. It lives on the surface 50 to 60 miles from shore and gradually works inshore as it approaches adult life. Toward the latter part of the summer the young fish, over an inch in length, moves from the surface to the bottom and seeks the sand, in which it burrows and spends the greater part of its life. With this information extensive towing work was undertaken, and through the kindness of Dr. Henry B. Bigelow, of the Museum of Comparative Zoology at Harvard University, and of W. W. Welsh and Lewis Radcliffe, of the United States Bureau of Fisheries, the results of the towings by the steamer Fish Hawk and the schooner Grampus were examined, and a few embryos of different sizes were found, from which the following results have been obtained. Recognition and thanks are also due to Dr. A. G. Mayer and his associates in the Carnegie Insti tution of Washington who have assisted in procuring these specimens.
In a few cases it was difficult to determine whether the embryos were Astroscopus larva or those of a nearly allied form, Kathetoskmata, which lives in deep water off the Atlantic coast; but since the adult Kathetos tomata has been studied and found to possess no electric organ, there remains no doubt that these embryos which possess the first rudiments of the electric organ are examples of Astroscopus. The embryos were all photographed before sectioning to aid in the identification of the species, but since Astroscopus guttatus and Astroscopus y-grwcum have very similar electric organs in the adult, it matters very little for this work whether the embryos are all of one species or not. Most of them have been identified as Astroscopus guttatus.