14U JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOI^. 11, NO. 6 



ENTOMOLOGICAL SOCIETY 



329th meeting 



The 329th meeting was held March 4, 1920, at the Cosmos Club, with 

 President Walton presiding and 21 memlDcrs and 3 visitors present. 



Program 



Wm. MiddeETon: Comparison of larval folds and adult sclerites in the 

 s aw- j lies. 



This paper dealt with the structure of the immature forms of Pteronidea 

 ribesii, treating especially the limits of a segment, the composition of its 

 tergum and pleurum, and the relations existing between larval and adult 

 parts. Particular attention was given to the transformation of the prepupa 

 to the pupa, and it was from observations during this phase of the meta- 

 morphosis that the indications of the homologies suggested were found. 



The structure of the saw-fly larval body was studied and it was concluded 

 that the segment is composed of four folds, three of which are armed and 

 always have a place in the exterior structure of the larva, and were shown to 

 develop into adult sclerites, while the fourth is never armed, is concealed 

 in some saw-flies, functioning as intersegmental skin, and was shown to be 

 represented in the adult also as a connective membrane. The folds are 

 defined by infoldings of the skin to which muscles are attached and the 

 muscles as well as the arrangement of these folds throughout the whole body 

 determine the limits of the segment. The interpretation of the segment thus 

 arrived at applies to the thorax as well as to the abdomen and to other saw-fly 

 larvae as was attested by several examples. 



The study of the metamorphosis brought out several interesting changes 

 in the prepupa preceding pupation, and the homologies were based on the 

 changes exhibited by prepupae under daily observations together with some 

 dissections of more advanced prepupae. Following a table of the homologies 

 the paper concluded with a brief summary of the more important evidence 

 supporting the homologies indicated and some suggestions as to the probable 

 causes of the changes in segment limitation between larva and adult. 



This paper was copiously illustrated by drawings showing the correlation 

 of the larval and adult structures. 



Discussion. — Mr. Rohwer noted that if the conclusions were correct this 

 was another case of unusual change in the thorax of the Hymenoptera. 

 When the first morphologist stated that the first abdominal segment became 

 a part of the so-called thorax of the Clistogastra there was some doubt in the 

 minds of many. This doubt was, however, easily disposed of by the presence 

 of the spiracle on the propodeum. The borrowing of part of the metanotum 

 of the larva by the mesonotum of the adult is not as easily proven as the 

 transferal of the first abdominal segment to the "thorax" of the Clistogastra. 

 When the composition of the adult mesonotum is considered, and especially 

 when its bulk is compared with the mesonotum of the larva such a transfer 

 does not seem unreasonable, and from the evidence furnished by saw-fly larvae 

 and adults it seems certain that Mr. Middleton's conclusions are correct. 



Notes and exhibition of specimens 



Mr. R. E. Snodgrass discussed the mouthparts and the alimentary canal 

 of the periodical cicada, on the basis of additional observations made since 

 his paper presented at the 327th meeting of this Society. The alimentary 

 canal of the adult cicada has an arm of the stomach forming a loop from the 



