No. I.] THE METAMERISM OF NEPHELIS. 57 



In Lumbricus, for instance, both the afferent and efferent 

 fibers of the central system, though somewhat more diffuse than 

 in Nephelis, run in well-defined bundles, and Miss Langdon (17) 

 has found numerous bipolar cells along these nerves. These 

 two elements, fibers and cells, necessary to form the inter- 

 muscular nerve ring of Nephelis are present in Lumbricus, 

 and when one takes into consideration the vast differences 

 between the life habits of the sluggish, mainly herbivorous, 

 earthworm and the active, free-swimming, carnivorous Nephe- 

 lis, it does not seem difficult to believe that specialization, so 

 far advanced among the leeches in other particulars, may so 

 combine these factors as to produce the result found in Nephe- 

 lis. This suggestion by no means excludes any other explana- 

 tion ; it is the one nearest at hand in the light of our present 

 knowledge. Recent investigations, with methylen blue espe- 

 cially, show that the peripheral bipolar ganglion cells connected 

 with the central system play an important part in the neural 

 system of some of the flat worms, and the whole matter of 

 peripheral nerve systems in this group, as well as that of the 

 annelids, is now in such a promising condition of investigation 

 that much light will, doubtless, soon be thrown upon it. 



The " Large " Nerve Cells. 



Investigators of annelid and arthropod nervous systems have 

 been familiar for a long time with certain nerve cells so large 

 in comparison with the ordinary motor cells of a ganglion that 

 they have often designated them by such words as "giant," 

 " colossal," and the like, and have described their location, 

 character, etc., without, so far as I know, bringing them into 

 any relation with each other. Such a relation exists in Nephe- 

 lis, though what its full signiiicance may be I do not yet know. 

 I find the large cells in a body somite arranged as follows : in 

 the ventral chain two "median" or "giant" cells within the 

 ganglion; in each connective between the ganglia lies a "colos- 

 sal " axial cell, which sends processes before and behind into 



" Fanny E. Langdon : " The Sense Organs of Lumbricus agriicola Hoffm." 

 Journ. of Morpk., vol. xi, 1S95. 



