324 THE AMERICAN NATURALIST. [Vol. XXXVII. 



the nuclei are semi-elliptical, lying with their long axes parallel 

 to the line separating the two cells. (Fig. 3 b.) 



In Machilis maritima, Oudemans ("87) describes four hypoder- 

 mal cells, but I am sure that there are but two in Machilis vari- 

 abilis. As Oudemans figures only a longitudinal section of the 

 ommatidia, it may be that he has made an error in observation 

 on this point, for in such a section, two cells present the same 

 appearance as four. 



The cone-cells. — In each ommatidium, proximad of the two 

 hypodermal cells, lie four long cone-cells (Fig. 3, c. c.) These 

 cells are in close contact along their entire axial surface, forming 

 a cone forty-five microns long with a diameter of seventeen 

 microns at its base or distal end. 



At its proximal end the cone is about two and one third 

 microns wide. Although these four cone-cells are closely 

 applied along their axial surfaces, yet their intercellular walls 

 are distinct in all transverse sections of the cone from its base to 

 its proximal end (Fig. 3 d and 3 e). 



At the extreme distal end of the cone, lie the granular and 

 deeply staining nuclei of its four cells, (Fig. 3, n. c. c.) In 

 transverse sections through these nuclei, each is seen to have the 

 same triangular form and size as that of the cells to which it 

 belongs, thus entirely filling its distal end. (Fig. 3 c.) In 

 longitudinal sections, these cone-cell nuclei appear to have their 

 greatest thickness over the centre of the cone and gradually 

 diminish in thickness toward the periphery. (Fig. 3, //. c. c.) 



The convex distal surface of these cone-cell nuclei fits into the 

 depression on the proximal surface of the two hypodermal cells. 

 (Fig- 3-) 



Whatever the substance of the cone cells may be, it is but 

 slightly affected by dyes. In most preparations it appears 

 absolutely unaffected by them, remaining a perfectly hyaline 

 structure. 



The distal pigment. — Surrounding the posterior two thirds of 

 each cone, is a sheath of pigment which appears black in masses, 

 but whose separate large round granules are maroon in color. 

 (Figs. 3 e, and 7.) Outside of this thin sheath of black pigment 

 and separating the cones of the different ommatidia, is a brown- 



