436 W. H. GASKELL. 



mater is interrupted by the passage of the fibres (/.) from 

 ghl^. to the ventral pineal eye {pn„.). I feel, therefore, inclined 

 to look upon the group of cells (ghl^) which form the ganglion 

 of Owsjannikow, and the cortex of the '' Zirbel-polster '^ of 

 Ahlborn, as the cortical layer of cells of the optic ganglion of 

 the ventral eye, while the nerve-fibres (/.) which pass from 

 them into the eye itself form the medulla and nerve of that 

 eye; the main part [ghl-^.) of the left ganglion habenula? being 

 formed of the cortical cells and medullary fibres which connect 

 this optic ganglion with its neighbour, and with the supra- and 

 infra-oesophageal ganglia. 



We see, then, that the original Crustacean-like ancestor 

 had a pair of median eyes each with its optic ganglion, and 

 its connections wath both supra- and infra-oesophageal gan- 

 glia; the right eye of the two remained functional longer 

 than the left, with the result of producing in the lamprey the 

 noteworthy asymmetery of the ganglia habenulse, and of the 

 two Meynert's bundles. 



I have no doubt but that further observation in the light 

 of the facts narrated in this paper will suffice to prove that the 

 pineal eye of lizards, &c., is also of the same kind as in the 

 Ammocoetes ; throughout the mistake of previous observers, 

 with the exception of Ahlborn, has been to rely too much 

 upon sections cut in the wrong direction, and to omit the 

 most important contents of the eye, under the delusion that 

 they were a coagulated albuminous fluid, and therefore due to 

 the method of preparation, and not essential elements in the 

 eye. 



Sect. — 9. The Structure of the Supra- and Infra- 

 oesophageal Ganglia. 



So close, indeed, is the comparison of the central nervous 

 system of the Ammocoetes with that of an Arthropod, that I 

 feel sure further investigation will bring out a complete coinci- 

 dence, not only in the topographical arrangement of the several 

 parts, but also iu histological structure. Such an investiga- 

 tion is now being conducted in the Cambridge Physiological 



