280 

 3. The Divided Eyes of Arthropoda. 



By Vernon L. Kellogg, Stanford University, California. 



eingeg. 17. März 1898. 



In the current number of the Zeitschrift für wissenschaftliche 

 Zoologie (Bd. 63. Heft 2) Dr. Carl Zimmer under the title »Die Fa- 

 cettenaugen der Ephemeriden«, p. 236 — 262, plates XII — XIII de- 

 scribes. the intimate structure of the divided eyes of the males of Chloe 

 and certain other genera oîEphemeridae. While it has long been known 

 that certain Jßpliem.eridae and other insects possess two pairs of com- 

 pound eyes , or one pair in which each eye has facets of two sizes 

 grouped in two fields separated by a more or less distinct line or con- 

 striction , the differences in finer structure between the members of 

 each pair of these divided eyes, or between the eye-elements of the 

 two regions of the quasi-divided eyes are first made known in Zim- 

 mer's paper. Chun^ has described the divided eyes oi Stylocheiron 

 and certain other genera of pelagic Crustacea, and has explained the 

 necessary physiological difi"erence of these morphologically different 

 optic fields. He offers also an explanation for the occurrence of the 

 two kinds of eyes among these marine Crustacea. 



In a recent study of the anatomy of Blepharocera capitata (a Ne- 

 matocerous Dipteren from North America) I have found a similar diffe- 

 rentiated condition of the compound eyes of both males and females. 

 Each compound eye has facets of two sizes grouped in two distinct re- 

 gions. By means of sections it is readily discernible that the omma- 

 tidia, or eye-elements of these two regions differ markedly. Those of 

 the region of larger facets, which is the upper and hinder part of the 

 eye , are conspiciously longer , larger and fewer in number than those 

 in the region of smaller facets , which is the frontal part of the eye. 

 In addition while the frontal region is strongly pigmented, the region 

 of larger ommatidia is very scantily pigmented. Without offering here a 

 detailed account of the structure of the eye-elements of the two regions 

 it is sufficient to say that the difi'erences in structure are essentially 

 those which distinguish an eye specially adapted for the perception of 

 moving objects from an eye of the more normal type. The special cha- 

 racters of the large-facetted region of the eye of Blepharocera agree in 

 the general tendency and character of their differentiation from the nor- 

 mal type with the large-facetted eyes of the pelagic Crustacea (Chun) and 

 the male Ephemeridae (Zimmer). In the males of Chloe and in several 

 pelagic Crustacea the variant eyes are fully adapted for the production 

 of »Superpositions-bilder«, a condition not reached in Blepharocera. 



1 Chun, Carl, Atlantis, Biologische Studien über pelagische Organismen, in 

 Bibliotheca Zoologica. Bd. 7. Heft 19, 1896. 



