CECIDOMYID^E. 9 



gated appendage whose use or homology is unknown. It 

 varies in shape in different species, the free end sometimes 

 terminating in two joints, sometimes in one, sometimes toothed 

 and serrated. This organ, discovered by von Baer, has been 

 called by Osten Sacken the "breast bone"; in England it is 

 known as the " anchor process ". By some it is thought to be 

 a pseudopod ; by others the mentum ; and Miss Ormerod be- 

 lieves 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 larva in its cocoon or case. 

 The motions of the larvae are usually slow, excepting those 

 which live on the surface of leaves. Those which change their 

 abode before assuming the pupa state become very active 

 about the period of metamorphosis. A very great activity 

 was observed by Winnertz 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 leav- 

 ing their galls. 



Owing to their rudimentary mouth-parts it seems evident 

 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 hermetically sealed and for the 

 most part with hard walls. It is probable that they absorb 

 nourishment in a quiescent state. As many as sixty individ- 

 uals have been known to live in a single gall. What causes 

 the galls is not easy to say ; probably some peculiar irrita- 

 tion produced by the insect. It is probable that the larvae 

 of Cecidomyia do not undergo moultings like most dipterous 

 larvae. Before assuming the pupa state some larvae leave 

 their galls and conceal themselves under ground, in dry leaves 

 and moss or under the bark of trees ; while others, on the con- 

 trary, complete their transformation within the gall itself. 

 The pupee are generally, but not always, enclosed in the cocoon, 



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