258 PROCEEDINGS OF THE AMERICAN ACADEMY, 



I come now to the consideration of the work which has been done 

 upon the sense organs of polychagte annelids by means of the newer 

 nerve methods. Retzius, working both with the Golgi method and with 

 methyleu bhie ia 1892, and confirming in 1895 his previous work, describes 

 for the epidermis of Nereis certain isolated sensory cells, which in almost 

 all the details of their structure and in their variations of form and posi- 

 tion show a remarkable resemblance to the cells of the sense organs 

 wliich I have described. I, however, have never found the cell body and 

 nucleus sunk beneath the deep ends of the epidermal cells into the under- 

 lying tissue, as Retzius has. I find some of the nuclei of the sensory 

 cells, it is true, at the most variable distances beneath the cuticula, even 

 as deep as the base of the epidermis, where they may lie immediately 

 above the circular muscles, either in an oblique position or parallel with 

 those muscles, and it not infrequently happens that such a nucleus is situ- 

 ated at some distance from the vertical axis of the sense organ to which 

 it belongs. 



For this apparent difference of condition between Nereis and the Mal- 

 danidoe, there are three possible explanations: — 



(1) The Maldanida3 studied by me may have had in the epidermis 

 isolated sense cells which did not respond to the blue method and were 

 consequently overlooked ; and on the other hand Nereis may have con- 

 tained sense organs similar to those of the Maldanidge, which did not 

 respond to the methods employed by Retzius. , 



(2) As Retzius used in his work only the Golgi and the methylen 

 blue methods, neither of which are especially favorable for the preservation 

 of the outline of the cuticula above the sense organs, he may have over- 

 looked any such indication of multicellular sense organs. Moreover, since 

 frequently only a single cell from such an organ stains with the blue, he 

 may have seen only such conditions and have consequently interpreted 

 them as isolated sense cells. 



(3) The epidermis of Nereis may differ so much from that of these 

 Maldanidie as to have only isolated sense cells, while the Maldanida? have 

 sense cells grouped into sense organs. This third supposition, however, 

 I think unwarranted. For although I have studied Nereis by means of 

 the removed cuticula only, I am convinced from the examination of this 

 cuticula that organs resembling those which I have described for the 

 Maldanidaj are likewise present in their integument.* 



* Since this part of tlie present paper was completed, tlie report of the meeting 

 of the American Morphological Society for December, 1896, has been received 



