THE STRUCTURE OF THE EYE OF SCUTIGERA 

 (CERMATIA) FORCEPS. 



JOSEPHINE HEMENWAV. 



GRENACHER ('80), in his article entitled " Ueber die Augen 

 einiger Myriapoden," described the structure of the eye of 

 Scutigera (Cermatia araneoidea). Briefly reviewed, his account 

 is as follows : 



Externally the eye of Scutigera has the appearance of a true 

 facet eye, consisting of one hundred of these "facets." To 

 each facet there corresponds an ommatidium. Each ommatid- 

 ium consists of a central crystalline body, surrounded by three 

 tiers of cells ; the distal tier of pigment cells, the middle and 

 proximal tiers of retinular cells secreting on their inner edges 

 a narrow band, the rhabdom. The crystalline body is com- 

 posed of very irregular segments. These segments may be 

 either cells or cuticular structures. In the adult eye they 

 cannot be regarded as cells, as nuclei are not found in them, 

 although Grenacher admits that at some time in their existence 

 they may have been cells, later becoming modified and losing 

 their nuclei. The possibility of their being secretion products 

 he does not admit, as he finds no cells to which their origin 

 could be traced. There are six to eight or nine of these 

 segments. 



The retinular cells with their rhabdoms embrace the proxi- 

 mal two-thirds or three-fourths of the crystalline body, the 

 posterior portion of the retinular cells reaching to the basal 

 membrane. Of the three tiers of cells surrounding the crys- 

 talline body, the middle tier, or outer retinula, is made up of 

 from nine to twelve cells ; the proximal tier, or inner retinula, 

 of three to four cells. Sections through the proximal layer 

 show that at this level the rhabdom is made up of four parts. 

 Toward the extreme proximal end of these proximal retinular 

 cells only three with their rhabdoms are visible in cross- 



205 



