vi ANATOMICAL SOCIETY OF GREAT BRITAIN AND IRELAND. 



connection, in the same way as the brain was closely connected with 

 the gut itself. 



The author then referred to the ctecal diverticula of the front part 

 of the gut in the Arachnids, and pointed out how a pair of such 

 anterior diverticula is present in such low Crustacean forms as Bran- 

 chipus, Artemia, etc. What is still more significant, the retinal 

 ganglion is so closely attached to the anterior extremity of the 

 diverticulum of each side as to be fused with its lining columnar 

 cells. In these animals these diverticula form nutrient channels, 

 especially for the important cerebral region. 



The author, therefore, concluded that the Trilobites, the nearest 

 living representatives of which are confessedly Branchipus, Artemia, 

 and Apus, possessed two nutritive anterior diverticula of the gut in 

 close relation to the two lateral eyes, and that by the more intimate 

 fusion of these two organs, doubtless for the purpose of nutrition, 

 the vertebrate lateral eye with its single-layered tube of columnar 

 supporting cells arose. He imagined, therefore, that the vertebrate 

 eye, with its inverted compound retina, owed its peculiarities to an 

 ancestor which was neither Arachnid nor Crustacean, as at present 

 defined, but partly Crustacean, so that the retina was compound ; 

 partly Arachnid, so that the retina was inverted ; in fact, to an animal 

 derived from the great Trilobite stock, such as was abundant on the 

 earth when the Cephalaspids made their appearance. 



