smith: eyes of pulmonate gasteropods. 267 



cells in the retina of one of the heteropods (Pterotrachea). He observed 

 that the cell, besides giving off a nerve-iibre, ends in two or more feet, 

 which pass between the bundles of nerve-fibres. Each foot is a great 

 tuft of parallel or branching processes, which pass through into the eye- 

 capsule. Such feet Grenadier called " radiculae," or rootlets, and in 

 his opinion they provide the cells with a special means of attachment. 

 Hesse, finding more than one proximal process on the unpigmented cells 

 of Helix, was reminded of Grenadier's figures, and he very properly 

 applied the same name to them, but did not describe the proximal part 

 of the pigment cells ; neither did he demonstrate that the radiculae of the 

 sensory cells passed into the capsule. Both Babuchin and Hilger described 

 the proximal branches of the pigment cells correctly, in my opinion, but 

 their error consisted in failing to trace the branches into the capsule. 

 Simroth's observations remain the only ones which were correct in this 

 matter. In this connection compare the three Figures, A, B (p. 235), 

 (p. 237), which I have copied from previous writers, with Figure D 

 (p. 256), which illustrates diagram matically the conditions as I have found 

 them in Limax. These radiculae are not " special " organs of attachment, 

 not being different in nature from the similar organs which the pigment 

 cells of the retina and the epithelial cells of the general surface possess. 

 From my figures of methylen-blue preparations, it is evident that the 

 radiculae of the sensory cells of gasteropods are quite different in appear- 

 ance from the structures so named by Grenadier. Although the radicu- 

 lae branch, they are not in any sense fascicles of parallel branches, but 

 even at some distance from the cell body each is single. Nearer the 

 capsule and, especially within it, there is a copious branching, somewhat 

 like a flat root-system. \Ve see, then, not only that the retina is a single 

 layer of cells, as is the external epithelium of the body, but also that it 

 is attached to a connective-tissue membrane in a similar way. It is not 

 possible to affirm that all of the sensory cells are so attached, for some- 

 times the smaller ones are more or less spindle-shaped and do not show 

 radiculae, although such may be present either hidden behind the cell 

 or invisible because unstained. 



The sensory cell, although narrow through the pigment zone, expands 

 at the base of the rod to become continuous with its core (Plate 1, 

 Fig. 4; Plate 2, Fig. 14). This condition explains the supposed fibre 

 which Babuchin described as occupying an axial position in the cell 

 between the nucleus and the " Ansatz." (See Fig. A, p. 235.) 



Previous investigators have found it difficult to depigment the retina 

 without entirely destroying the sections. But depigmentation is easily 



