152 Miscellaneous. 



tliemselves into a rich plexus. From the principal cords and from 

 the anastomoses issue numerous very fine filaments which anasto- 

 mose among themselves so as to form a network with square or 

 rectangular meshes. The nerves are composed of the same fine 

 fibres as the commissures of the central system. 



Sense-organs. — Besides the otoeyst, notwithstanding what Graff" 

 has said, there exist two eyes, represented by two yellow pigment- 

 spots, and I have recognized the existence of a new sensitive appa- 

 ratus which I shall name the fronted organ. It is an ovoid, clear, 

 refringent mass, situated at the superior terminal extremity. It 

 measures about 0-04 millim. by 0*03 millim. The larger end of the 

 ovoid is situated at a small distance from the highest commissure of 

 the nervous system, or even reaches it ; the smaller end is applied 

 against the integuments, which, at this level, are destitute of cilia 

 and furnished with short conical papillae regularly arranged. The 

 mass is bounded at the sides by a double layer of ganglionic cells. 

 A small number of cells of the same kind exist in its interior. 

 From the bounding cells, the central cells, and the nervous commis- 

 sure start numerous very fine filaments which anastomose in the 

 refringent mass and form a network ; then the filaments gradually 

 approach other and converge regularly towards the superior extre- 

 mity, where they terminate each in one of the papillse mentioned 

 above. In a great many cases I have been able to trace the fila- 

 ments from the cells in which they originate to the terminal papilla. 

 The refringent matter performs the function of a sustaining sub- 

 stance. The whole apparatus is very mobile, and the animal seems 

 incessantly to feel about with the papillae which terminate it. 



In voung Convolutce just hatched and still destitute of zoochlo- 

 rellae the frontal organ exists even more highly developed in propor- 

 tion than in the adults, and I have been able to demonstrate the 

 nervous system, which is constituted as in the adult, but less 

 condensed and less rich in ramifications. 



Lacunce of the Reticulum. — The nerves appear everywhere sur- 

 a'ounded by an endothelial sheath, the cells of which, smooth and 

 riattened on the side towards the nerve, are continuous externally 

 with those of the reticulum. The cavity included between the 

 nerve and its sheath is not entirely virtual. By means of a certain 

 reagent which I shall make known we can demonstrate the existence 

 of a cavity between the nerve and its sheath, and this cavity is 

 ■continuous throughout with a very highly developed system of 

 lacunae, which occupies the whole of the zoochlorella-layer. Each 

 of these Algae is enclosed in a free cavity, and the spaces interposed 

 between these cavities are formed by the lacunae in question. More 

 circumstantial details upon this point will be given in my forthcoming 

 memoir. 



The German zoologists have reproached M. Blanchard with having 

 injected the nervous system of the Planarine, and described this 



