390 MR. B. THOMPSON LOWNE ON THE COMPOUND VISION 



hoek had long before observed the images produced by the individual facets. Gottsche 

 observed and drew attention to these : he, I believe, was the first who investigated the 

 structure of the great rods (Sehstabchen), and suggested that the highly refractive axial 

 threads, which he discovered in their interior, in some way transmit the images formed 

 by the lenses to recipient nervous structures beneath. 



I can hardly imagine that the earlier writers intended to convey the idea that an image 

 could be transmitted, as Dr. Grenadier facetiously suggests *, " as a message is trans- 

 mitted by a telegraph wire," but suspect that they meant that rays of light from certain 

 definite points in the image are so transmitted. There is, however, considerable 

 ambiguity about Gottsche's paper on this and other points, although he apparently 

 correctly indicated the position of the true recipient layer, beneath the great rods, 

 without actually observing it. 



Gottsche's paper appears to have been completely misunderstood by all his critics, 

 who seem to have imported into it a false analogy between the image in the compound 

 eye, and that in the vertebrate eye : the image is thus supposed to fall upon the retina. 

 If Gottsche had intended to convey such an idea his view would have been, as it is 

 generally supposed to be, in direct antagonism to Midler's hypothesis; yet Miiller 

 gave a kind of adherence to Gottsche's view, holding it to be consistent with and supple- 

 mental to his own. 



It appears to me that the whole tenor of Gottsche's paper is an attempt to modify, not 

 to destroy, Midler's theory, although both he and Miiller, in the note which accompanies 

 this paper, seem to have forgotten the difficulty which arises from the inversion of the 

 subcorneal image. And further, Gottsche's retina is not the retina of Wagner, Ruete, 

 and Dor. Soon after the publication of this paper Leydig t drew attention to the con- 

 tinuity of the axial structures of the great rods and the crystalline cones ; and supposed the 

 cones to be the terminal organs of the optic nerves. His views on the connexion of the 

 cones and the nerve-centre are not easy to comprehend, as he appears to deny the truth 

 of Midler's hypothesis, at the same time that his observations apparently support it. 



ClaparedeJ then pointed out the apparent continuity of the cone and the corneal 

 facet, in Typhis, and found that the cornea, cone, and axis of the great rod, in some 

 insects, consist of the same material ; he asks, if it is not possible that these are all con- 

 cerned in transmitting the image to nervous structures beneath them. 



In criticizing the views of Gottsche, Claparede, and Leydig, it appears to me that it 

 should constantly be borne in mind, that they worked at a time when the close relation 

 between physical and vital phenomena was less completely understood than at present, 

 and that they consequently, perhaps unconsciously, ascribed hypothetical vital properties 

 to structures, which will not bear rigorous investigation. 



Max Schultze § first investigated the optical relations of the great rods, and concluded 

 that they are not the terminal organs of the optic nerve, after a most laborious exami- 

 nation of their structure. He also rejected Mailer's hypothesis as optically untenable. 



* Untersuchungen iiber das Sehorgan der Arthropoden, p. 10. Gottiugeri, 1879. 



t Miiller's Arohiv, 1855', p. 406. X Zeitschrift fur wissensch. Zool. Bd. x. 



§ Schultze, Arohiv, Band ii. p. 404. 



