I20 NORTH AMERICAN DIPTERA. 



the jaws are rudimentary and there are large two-jointed 

 palpi or antennae. The last abdominal segment is smooth 

 and rounded, sometimes with tubercles or a pair of horny 

 processes which are said to be used by the larvae in leap- 

 ing. On the under side of the body at the junction of 

 the first thoracic with the supernumerary segment there 

 is a horny, more or less elongated appendage whose use 

 or homology is unknown. It varies in shape in different 

 species, the free end sometimes terminating in two points, 

 sometimes in one, sometimes toothed and serrated. This 

 organ, the spathula stcrnalis of Mik, has been called by 

 Osten Sacken the 'breast bone'; in England it is known 

 as the 'anchor process'. (See figure of Diplosis pini-radi- 

 at<c). By some it is thought to be a pseudopod; by others 

 the mentum; and Miss Ormerod believes its function is 

 that of a scraper or digger in obtaining food from the 

 stems. More probably its use is for locomotion, or for 

 changing the position of the larvae in its cocoon or case. 

 The motions of the larvae are usually slow, save of 

 those which li\*e on the surface of leaves. Those which 

 change their abode before assuming the pupa state be- 

 come very active about the period of metamorphosis. A 

 very great activity was observed by Wiunertz in some 

 such larvae after a thunder storm. They left their hiding 

 places under ground and crawled about restlessly for 

 some time; repeating these actions after every thunder 

 storm, some even two months after leaving their galls. 



Owing to their rudimentary mouth-parts it seems evi- 

 dent that the larvae must feed upon juices only, and that 

 they need very little nourishment is shown by the fact 

 that they attain their full growth and development in a 

 gall just large enough to enclose them, apparently her- 

 metically sealed and for the most part with hard walls. 

 It is probable that they absorb nourishment in a cpuiescent 

 state. As many as sixty individuals have been known 



