1 912] Morphology and Biology of Insect Galls 363 



food, and it immediately attacks and devours the juicy tissue with great 

 avidity. The cells which are demolished, wonderful to relate, are replaced 

 almost at once. The cells of the gall pith remain capable of division as 

 long as the larva in the chamber requires food, and the surface cells which 

 have been devoured in the gall chamber are soon replaced by new cells." 



Kiistenmacher^^ has advanced an entirely different view and his 

 opinion may be taken as representing the theory of the other school of 

 observers. 



He states, — "Die im Innern entschlupfte Larve, welche ihren Tisch 

 reichlich gedeckt findet, beisst die innern Zellen des Nahrungsgewebes, 

 welche lose, von der Eiweiss-Zucker-Oel-Emulsion strotzend, hervor- 

 ragen, an und saugt dieselben regelmassig ringsherum aus, wahrend die 

 sehr dunnen Wandungen schmal schlauchartig iibrig bleiben." 



In deciding between these two theories the question to be answered 

 is, does the larva eat both the walls and contents of the cells as stated by 

 Kerner, or does it extract in some way the contents of the cells, leaving 

 the walls practically intact? Several different points are involved in 

 the discussion of this question, (a) The absence of frass in the larval 

 chamber, (b) The completeness of the alimentary canal in the larva. 

 (c) The nature of the stomach contents, (d) The presence of collapsed 

 tissue and empty cells in the nutritive zone. 



When a mature Cynipid gall is examined the larval chamber, in 

 which the producer has passed through its early stages, is found unsoiled 

 by excrement. Concerning this matter my observations agree with 

 those made by Walsh in respect to the Cecidomyia larvae. By way of 

 comparison, if a mature gall is examined, the larva of which is known to 

 eat the entire cells, a comparatively large quantity of excreted material 

 is found (Fig. 68) . The mature larva and its frass from a gall of Pontania 

 pomum Walsh were dried in a desiccator and weighed. The following 

 result was obtained : 



Larva .0115 gm. 



Frass .0319 gm. 

 In view of the comparatively large amount of frass in the sawfiy gall, its 

 absence in those of the Cynipidae appears significant. 



This fact concerning the larvae of the Cynipidae has not received 

 attention since it has been supposed that the intestine of the Cynipid 

 larva ends blindly. Comstock^^ makes the following statement on this 

 point: "The larvae are maggot-like and without a caudal opening to 

 the alimentary canal." Serial sections were made of the larvae of the 

 producers Philonix nigra Gill (Fig. 61), and Amphibolips confluens Harris 

 (Fig. 62). These sections prove conclusively the completeness of the 



