LEWIS. — POLYCH^TE ANNELIDS. 255 



But many cells show an oblique direction of the long axis with reference 

 to the cuticula (see Plate 6, Fig. 38, and Plate 7, Fig. 51). It is evi- 

 dent that ordinary methods of staining would be very unsatisfactory for 

 the discovery of these oblique cells. 



(8) That in many respects the sensory cells of these epidermal sense 

 organs show a remarkable resemblance to those described by Retzius 

 ('92, '92% and '95) for Nereis. The chief point of difference is, that 

 Retzius found isolated sensory cells in the case of Nereis, whereas in the 

 case of these Maldanids the sense cells are grouped into definite sense 

 organs. Is it not possible that the conditions seen and figured by Retzius 

 may be accounted for without concluding, as Retzius has done, that 

 sensory cells exist in the epidermis of Nereis as isolated single-cell 

 organs ? Is it not possible that Retzius, through failure to control his 

 observations by sections made after the more ordinary methods of treat- 

 ment, overlooked the fact that such apparently isolated cells really 

 belonged to a multicellular sense organ ? 



(9) That the epidermal sense organs here described can be observed in 

 the living worm into which methylen blue has been injected, the 

 worm being placed in a shallow dish of sea water, and examined even 

 under a comparatively low power of the microscope. 



(5) Function of Sense Organs. 



Regarding the function of these sense organs, I have little to suggest 

 save of a negative character. 



The fact that they are found at all parts of the surface of a worm 

 inhabiting a tube would seem to be against the supposition that they are 

 organs of taste. In such a worm organs of taste would be of little service 

 except at the anterior region of the body. The same argument may be 

 made against the supposition that they are organs of smell. 



Certain facts seem to favor the supposition that they are tactile organs. 

 That the worm is sensitive, even in the posterior region of the body, is 

 shown by pinching or pricking the tail as it projects from the sand tube 

 which it inhabits. Again, we find the organs especially numerous upon 

 exposed or elevated parts of the body. 



Spengel, who found similar organs, but only in the mouth region of 

 certain marine annelids, held them to be organs of taste on account of 

 their position in the mouth ; but this reasoning could not hold for organs 

 found in other regions of the body. It is not impossible, of course, that 

 in the region of the mouth such organs function as organs of taste, and in 

 other parts of the body as tactile organs. 



