smith: eyes of pulmoxate gastekopods. 



235 



and molluscs could not be cuticular, and gave the first significant inter- 

 pretation to the fibrillations of the retinal elements. Although he still 

 held, in a vague way, to the cuticular conception of the rod-zone, he 

 initiated the interpretation which regards as untenable the idea, that 

 the recipient organs of the retina can be inert matter; in support of his 

 belief he found an astonishing abundance of what he termed neurofibrils 

 in the rod-zone, as well as in the deeper layers of the retina. On the 

 whole, however, little confidence can be placed in Patten's neurofibrils, 

 for the following reasons : (1) he used a method which in itself is not 

 suited to the differentiation of histological details; (2) a maceration 

 which will dissolve cuticula cannot be expected to leave the delicate 

 nerve fibrils intact; and (3) Hesse, who has recently reinvestigated the 

 eye of Haliotis, one of the forms on which Patten worked, does not con- 



stm. 



Fig. A. Helix pomatia, after 

 Babuchin. ps., Pigment cell, thought 

 to'be sensory; a., " Ausatz." 



pz. 



Fig. B. Helix pomatia, after Hilger. stm., 

 Rod-mantle; ps., pigment cell; stz., rod-cell; 

 both kinds of cells considered sensory. 



firm his observations. Nevertheless, as there is, according to Hesse, a 

 delicate, brush-like rod on the sensory cells of the retina of Haliotis, 

 Patten probably saw some indication of it in his preparations. Patten's 

 studies of neurofibrils preceded those of Apathy by more than a decade, 

 and he was therefore, consciously, the pioneer in a new field, namely, the 

 study of the finer elements in the peripheral endings of the nervous sys- 

 tem. He recognized the significance of the discoveries of Babuchin and 

 Hensen as they themselves did not. He pointed out the futility of con- 

 sidering the presence or absence of pigment a criterion for judging of the 

 sensory character of the retinal cells. 



Parker ('95) gave the death-blow to Grenacher's theory, that the 

 recipient elements in the eyes of arthropods are cuticular, when he 

 showed that the rhabdomes of the eyes of the crayfish are made up of 

 neurofibrils from the retirmlar cells. Thus, the erroneous notion that 



