The Origin of the Electric Organs in Astroscopus Guttatus. 151 



to those mentioned above were found on the same muscles and with 

 the same topographical relation to the muscle-cells. They had the 

 same dense stain, but were very much smaller in area, as indicated in 

 figure 1 of plate v. 



A few embryos of the species Batrachus tau were then sectioned in 

 order to observe the muscle-tissues, as it was thought possible that the 

 smaller and more numerous cells might represent the generating area 

 of the muscle itself and have no connection with the electric tissue. In 

 these embryos such areas were found on several of the muscles, but a 

 very interesting point lay in the fact that in every case this area of 

 generating tissue lay on the opposite side of the muscle from that on 

 which the electric organs of Astroscopus are derived, i. e., on the side 

 toward the eye-ball. In Astroscopus, however, this area corresponds 

 in every case with the position from which the electric organ is to be 

 generated; moreover, no such areas could be found in Astroscopus on 

 the muscles not forming electric tissue. For this reason I feel certam 

 that the darkened areas represent the first beginnings of electric tissue. 

 The possibility also arises that in the darkened areas on the muscles of 

 the young Batrachus we may have a step in the evolution of the electric 

 organs in the toad-fish group. 



The innervation of the eye-muscle in the 9.5 mm. embryo is perfectly 

 normal and no nerve-endings are seen even to approach the electric 

 tissue. A resume of the normal eye-muscles, their origin, insertion and 

 innervation will here be given for reference (Herrick 61 and Wieders- 

 heim 94) . The eye-muscles are six in number — rectus internus, exter- 

 nus, inferior, and superior, and obhquus inferior and superior. 



The rectus internus, externus, and superior originate in the subcra- 

 nial canal at the extreme caudal end of the basioccipital. The rectus 

 externus originates in the extreme caudal end of the canal and runs 

 dorso-laterad to its insertion on the base of the eye-ball. It receives 

 the entire abducent or sixth nerve. 



The rectus internus originates near the caudal end of the canal in a 

 groove on the dorsal side of the parasphenoid bone and runs along the 

 inner sides of the orbits to its insertion on the cephahc border of the 

 eye-ball. It receives a branch of the oculomotor nerve, or the third 

 nerve. 



The rectus superior originates in the cephaUc end of the subcranial 

 canal from the parasphenoid, under the rectus internus, and from the 

 membranous roof of the canal over the same. It runs close to the 

 rectus internus to the end of the canal, turns dorsal and laterad, and 

 crosses the rectus inferior and optic nerve to reach its insertion. It 

 receives a branch of the oculomotor nerve. 



The rectus inferior arises from the basisphenoid bone and runs over 

 the rectus internus, rectus superior, and optic nerve to its insertion. 

 It receives a branch of the oculomotor. 



