1912] Blackmau — Supernumerary Median Ocellus 93 



two lateral ones, lying more dorsally, and a single median one. 

 This arrangement is subject to considerable variation and even 

 the number is not constant for the entire class. There may be 

 only two present (Lepidoptera, etc.) or only one, and indeed in a 

 number of cases (Dermaptera, Locustidse, Coleoptera, some Honi- 

 optera,and some Lepidoptera), the ocelli may be entirely absent 

 in the adult. So far as the writer knows the ocelli are never more 

 numerous than three except in immature forms, degenerate para- 

 sitic forms, and in certain of the very lowest insects in which groups 

 of ocelli take the place of the compound eyes. In the pupal stage 

 of Bombus the median ocellus, according to Packard^ possesses "a 

 double shape, being broad, transversely ovate and not round like 

 the two others, as if resulting from the fusion of what were origi- 

 nally two distinct ocelli." In accordance with this we might ex- 

 pect to find a pair of median ocelli or at least a transversely ovate 

 one in the adult or nymphal stages of lower insects. Such, how- 

 ever, is not the case except possibly in other members of the order 

 Hymenoptera where as will be mentioned later the structure of 

 tbe nervous connections are such that we might expect occasional 

 double median ocelli in the immature stages and possibly even in 

 the adult. 



The normal number of ocelli in the short horned grasshoppers 

 is three, arranged in a triangle, the two dorsal ones being lateral 

 and near the inner margin of the compound eye, while the ventral 

 ocellus is median in position ventral to the antenme. In a num- 

 ber of years experience with grasshoppers in laboratory work with 

 large classes the writer has never seen any variation in the number 

 or relative position of these ocelli. Last fall, however, an adult 

 female specimen of Melanojjlus femur-riibrum was brought to me 

 by one of my students which possessed two median ocelli instead 

 of the ordinary single one. As I had never seen or heard of such 

 an anamoly, the specimen was preserved for further study. 



The accompanying photograph reproduced at a magnification 

 of about five diameters shows the conditions better than would a 

 lengthy description. The two median ocelli will be plainly seen 

 placed symmetrically one on each side of the median line. Each 

 is approximately circular and apparently perfect in every respect. 

 Each one as far as could be observed is but slightly smaller than 



iPackard A. S. Text Book of Entomology Maemillan Co., New York (1S9S). 



