PROCEEDINGS, 1917. 43 



ings is another point which needs careful investigation. Considerable work was done 

 on this problem in connection with the Lepidoptera, by W. H. Jackson (3) 



This by no means exhausts the number of interesting points raised in connection 

 with a study of the pupa. A study of pupal morphology should throw some light on 

 the homology of various larval and adult structuies. A great deal of information re- 

 garding the development and disappearance of sutures may be obtained from this study. 

 It has also been of considerable help in homologizing mouth parts. 



As regards the classification of the pupae very little has been done. This is true of 

 all immature stages and particularly true of the pupa. A classification of the pupae of 

 various orders may be of usein two ways; first, byenablingone to recognize the insects 

 in this stage; and second, by showing relationships between groups or individuals not 

 to be obtained from the other stages and thus putting our classification on a firmer 

 basis. It seems more and more apparent, after one studies immature stages of in- 

 sects, that these should be used to assist in developing schemes for classification and 

 that a classification based entirely on adult characters often fails to show true relation- 

 ships. 



As regards the classification of pupae for the purposes of recognition very little 

 has been done, or at least published. There are no keys to the orders, so far as I am 

 aware, and a student who collects pupae must have a broad experience in breeding in- 

 sects to know even to what order his collections belong, much less family or genus, un- 

 til he has waited for the adult to emerge. In the different orders there is very little ac- 

 complished. A start has been made in the Lepidoptera (4) and Diptera (5) but other 

 orders are parctically untouched. Often it is most advantageous to be able to deter- 

 mine the pupa, especially in the case of imported nursery pests. 



In some cases where species are closely related, the pupae may be found to possess 

 better characters for identifying the species than either larvae or adults. This is well 

 known to be true of certain chironomids. It is also true of certain genera of Lepidop- 

 tera. 



Aside from the classification of pupae merely for the purpose of identification 

 there is a more important phase of the subject which has scarcely been recognized. 

 There are many who have little faith in a classification which considers characters of 

 the immature stages as well as those of the adult. They argue that the adult must be 

 the final and determining factor in classification, because of the many modifications 

 of the immature forms to suit changing conditions of life. Is this not true of the adults? 

 Many closely related species have very different modes of life and the resulting modi- 

 fications so fit them for these changed conditions. If lack of modifications is a factor of 

 importance in classification, then surely in the pupa we have the stage in which the least 

 possible modification takes place. The matter of obtaining food is entirely eliminated, 

 so no modifications are necessary for that purpose. Comparatively few pupae are in 

 any way changed for purposes of protection or mimicry, since the majority are found 

 in cocoons or in the soil. The number of pupae modified for the purpose of obtaining an 



3. Morphology of the Lepidoptera. Trans. Linn. Soc. London, Zool., Ser. 2, 

 Vol. 5. 



(4) (a) T. A. Chapman. Some neglected Points in the Pupae of the Heterocerous 

 Lepidoptera. Trans. Ent. Soc. London, 1893, p. 97-119. 



(b) A. S. Packard. Attempts at a new classification of the Lepidoptera. Mono- 

 graph of the Bombycine Moths of America North of Mexico, Part I, Memoirs National 

 Academy of Sciences, Vol. 7, p. 56-83. 



(c) Butterflies of the Eastern United States and Canada, 3 vols. 



5. J. R. Malloch, the Chironomidae or Midges of Illinois. Bull. III., St. Lab. 

 Nat. Hist. Vol. X. 



Also a Preliminary Classification of Diptera, Part 1, Bull. III. St. Lab. Nat. His- 

 tory, Vol. XII. 



