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very closely the description given by Mai er and other writers. The 

 visual cells, called by various wiiters, »Glaskörper«, »Glaskörper- 

 kugeln«, and »lichtpercipierende Zellen«, are arranged in a 

 single layer around the axial nerve-fibers. The symmetry of this ar- 

 rangement is broken at the upper end on one side by a multiplication 

 of the visual cells , so that the layer there may be two or three cells 

 thick. A point not mentioned by Mai er is the fact that in the ante- 

 rior eyes this multiplication of clear cells takes place at the upper an- 

 terior side , while in the posterior eyes the upper posterior side con- 

 tains the surplus cells. The visual cells contain a large crescentic or 

 horse-shoe shaped vacuole surrounded by a layer of protoplasm, in the 

 most thickened part of which the small nucleus is placed , as first 

 pointed out by Prof. Whitman. The visual cells are surrounded by the 

 pigment layer. In young specimens with completely developed eyes, 

 having the pigment decolorized by hardening in picro-sulphuric acid, 

 the pigment layer is found to be made up of a single layer of small 

 quadrangular cells containing small, not very distinct nuclei, centrally 

 placed. Outside the pigment layer is a layer of connective tissue. The 

 position of the pigment cup leaves an opening at the upper part of the 

 eye and at one side , and it is at this opening that the tactile cells are 

 found. Over the top and at the side of the pigment cup, the epider- 

 mal cells become elongated to two or three times their normal length. 

 Their nuclei are smaller than those of the clear cells and situated at 

 the base of the cells. These cells are the homologues of the cells dis- 

 covered by Prof. Whitman in Clepsine and Nep he Us , and probably 

 possess the same sense hairs. I have sectioned a few specimens of the 

 Japanese land leech Haemadipsa japonica and find elongated tactile 

 cells above the clear cells. They are much longer and more numerous 

 than Prof. Whitman's drawing of the land leech would indicate, 

 and are more symmetrically arranged than in Macrohdella. The ar- 

 rangement of visual cells is perfectly symmetrical, as shown by Prof. 

 Whitman. I have not thus far been able to discover any loose or 

 over crowded arrangement of visual cells. In Prof. Whitman's 

 drawing of the land leech, the nerve is represented as entering at the 

 side and not the base of the eye, as shown by M ai er. I find the nerve 

 in both positions in Macrohdella and Atdostomum, but have not decided 

 whether it is peculiar to anterior or posterior eyes. The nerve of the 

 eye in all specimens examined has two branches as indicated by 

 Mai er. 



