326 THE AMERICAN NATURALIST. [Vol. XXXVII. 



micron in width. The rhabdoms are fluted, having in trans- 

 verse sections the form of a seven-pointed star (Figs. 3 g, and 7). 



In sections from which the pigment has not been removed, 

 the rhabdoms appear as perfectly hyaline structures, while in 

 depigmented and stained sections, with the except] f a all 

 central core, they invariably appear non-granular and deeply 

 staining. (Fig. 3, and 2). Thus the rhabdoms present a 

 decided contrast to their cones which are but slightly affected 

 by dyes, if at all. 



There has been no indication in any of the sections that the 

 rhabdoms consist of seven parts or rhabdomeres, except that in 

 cross section they appeared as seven pointed stars. (Figs. 7 and 

 8.) 



In many longitudinal sections they often have a peculiar 

 beaded, or sometimes a corkscrew appearance. (Fig. 9.) This 

 peculiarity has been noticed in sections so differently treated 

 that, at first, it seemed as if it must be due to the presence of 

 nerve fibres in the rhabdoms but it now seems that it is prob- 

 ably an artifact. 



That the cones and rhabdoms are in Machilis distinct and 

 separate structures, is evident for three reasons: — first, the 

 rhabdoms always appear as deeply staining structures, while the 



circular in outline and divided into four parts or cells while the 

 rhabdoms invariably have the form of a seven-pointed star; 

 third, in longitudinal sections there is always a distinct trans- 

 verse line where the cone-cells end and the rhabdoms begin. 

 (Figs. 2 and 3.) Then, too, in many sections, the cones appear 

 partly broken away from the rhabdoms at this point and when- 

 ever the cones were entirely separated from the rhabdoms, the 

 break invariably occurred at this particular point. (Fig. 5.) 



This is a very different condition from that which exists in the 

 lobster's eyes as described by Parker ('90), where the four cone- 

 cells are continued as fibers outside of the rhabdom to the base- 

 ment membrane. It also differs materially from the condition 

 found in the eyes of Mantis (Patten '86), where the cone-cells 

 extend to the basement membrane through the centre of each 

 ommatidium, there being no distinction between cone-cells and 

 rhabdom. 



