492 SYNOPTIC COLLECTION. 



The Cecidomyidae or gall gnats are among the more 

 specialized forms of the Orthorhapha. The larva of one 

 species of Cecidomyia (C. strobiloides) makes the pine- 

 cone willow gall (No. 1259) which resembles strikingly 

 a pine cone. The gall is really a deformed bud produced 

 by the larva which lives within the gall until ready to 

 transform. 



The Hessian fly, Cecidomyia destructor Say, (PL 1260, 

 figs. 1-4) differs from Cecidomyia strobiloides, since its 

 larva does not make a true gall. This larva (fig. i) has 

 the head and mouth parts in such a vestigial condition 

 that it absorbs its food, which is the sap of the wheat. 

 When ready to transform, its skin becomes hard, brown, 

 and unsegmented. The pupa (fig. 2, ventral view) 

 within this hardened case or puparium (fig. 3) remains 

 absolutely motionless. On account of the resemblance 

 of the puparium to a flax seed this is known as the 

 "flax seed state" of the insect. The presence of these 

 "flaxseeds" between the leaf and the stalk of the wheat 

 causes the stem to swell and the leaves to die (Packard) 

 and thus in both the larval and the pupal stage the insect 

 does great damage to the wheat crop. 



It is interesting to note that in this Dipterous family, 

 the Cecidomyidae, there :, an extremely interesting form, 

 Miastor, whose larvae are capable of laying eggs. Here 

 is a case where it would seem that the law of acceleration 

 in development has acted so that the egg-laying habit 

 peculiar to the adult stage in most animals has been car- 

 ried back to the larval stage. 



The next division of flies, the Cyclorhapha, are more 

 specialized than the Orthorhapha, both in the larval and 

 adult condition. The group is represented by the flesh- 

 fly. Sarcophaga (No. 1261); and the house-fly, Musca 

 domestica Linn. (No. 1262). The larva or "maggot" of 

 Musca is more reduced than that of Tabanus. The head 

 has nearly disappeared, and the mouth parts exist as mere 

 vestiges. 



