154 ENTOMOLOGICAL NEWS [June, '20 



instances, on the other hand, when such exceptions occur 

 quite constantly throughout the members of an entire order, 

 or similar larger subdivision of a group of insects, these ex- 

 ceptions become of sufficient importance to merit a reference 

 to them, especially in an article intended for general reference, 

 such as Dr. MacGillivray's paper on "The Eyes of Insects."* 

 I would therefore call attention to one or two statements in 

 Dr. MacGillivray's article which might be misleading to 

 anyone not familiar with the subject, although the main points 

 of the article are quite correct, and are well taken. 



Dr. MacGillivray's claim that "the developing compound 

 eyes of the adult can frequently be seen in the pupa of ento- 

 metabolous insects and rarely in their larv^ae, but these stages 

 are never provided with functional compound eyes" would 

 appear to be too sweeping a statement, since exceptions to 

 this rule occur quite constantly throughout the members of 

 an entire order of insects, and a few scattered instances are 

 to be found in other orders. Thus, all known lar\ae of in- 

 sects belonging to the order Mecoptera have functional com- 

 pound eyes, and in full-grown larvae of certain corethrid 

 Diptera the compound eyes are so large and well-developed 

 that it is difficult to believe that they are not functional. 



It is evident that Dr. MacGillivray jneans functional ocelli 

 when he states that ocelli are present "only in the adults of 

 exometabolous and entometabolous insects," but when one 

 examines the ocelli of a young grasshopper, for example, they 

 appear to be quite as capable of functioning as those of the 

 adult. While it is possible that the statement that "func- 

 tional ocelli are never present in nymphs, larvae, or pupae" 

 may be correct, it would have been much more convincing 

 if some proof had been presented in support of this view. 

 As was mentioned above, the ocelli of a grasshopper nymph 

 have every appearance of being as capable of functioning as 

 those of the adult, and it is difficult to believe that the ocelli 

 of full-grown nymphs of our larger Plecoptera, certain may- 

 flies, etc., are wholly functionless. The ocelli of the latter 

 forms are quite large, and would appear to be capable of dis- 

 tinguishing light from darkness — which is the function as- 



* Ext. News, xxi, 97-100, April, 1920. 



