330 jS. WATASE. 



the nucleus (xV) anil the optic nerve fibre (0/).«), shows a charac- 

 teristic mariv of the cell. A zone around the nucleus (JV) shows 

 concentric markings. Longitudinal striae run through the axial 

 process and the optic nerve; {Ejf) an attenuated epithelial cell. 

 3(EX2)Z. 



Fig. 14. Another type of the central ganglion cell. Pigment 

 patch is greatly extended; nucleus (iV) is eccentric; (£"/;) attenuated 

 epithelial cells. 3(Ex2)Z. 



Fig. 15. The central ganglion cell, with its axial ]irocess (Ax.p) 

 divided into several branches, by some mechanical causes. All these 

 branches are longitudinally striated like the nuiin one and would 

 seem to be made up of a collection of extremely fine longitudinal 

 fibrils. Two pieces of chitinous body {Rh) are found at the junction 

 of the axial process and the cell-body proper of the ganglion cell. 

 They appear to be fragments of the rhabdomeres. S (E X 2) Z. 



The specimens figured in Figs. 10-14 were treated with Haller's 

 macerating fluid; that shown in Fig. 15 was treated with sulphuric 

 acid, 8 drops to 30 grams of water. 



Fig. 1G. Epithelial cells isolated from the margin of the omma- 

 tidial dei>ression. The part in which there is no pigment is turned 

 outward and comes in direct apposition to the chitin. 



Peate XXXI.— Limulus, Homarus, Cambarus, Squilla, Callinecies, 

 iSerolis. 



Figs. 17-3.3. — Limulus. This series of specimens is intended to 

 show the range of modification of the epithelial cells found in the 

 ommatidium and its direct neighborhood. 



Fig. 17. Central ganglion cell with several attenuated, non- 

 pigmented epithelial cells. J (E X 2) Z. 



Fig. 18. Retinula cell with a few pigmented epithelial cells at its 

 side. J (E X 2j Z. 



Figs. 19-33. Ordinary epithelial cells isolated from the omma- 

 tidial region, i (E X 2) Z. 



Fig. 34. — Homarus. Retinulae partly isolated. Each retinula 

 secretes a chitinous body which assumes a serrated appearance 

 CRb). This is the rhabdomere; when the bundle is brought together 

 it assumes a spindle shape. The upper part of each retinula cell is 

 free from pigment, and is connected with the pigmented portion by 

 a long, slender neck. The nucleus of the retinula is situated at the 

 non-pigmeuted, distal extremity, ii (1) X 2) Z. 



