30 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



different forms of galls, and we may be nearly sure 

 that there are as many kinds of morbid poisons 

 produced by gall insects, each form answering to a 

 different virus."* 



It is certain that there is no positive evidence 

 tending to show that the implied differences in the 

 composition of the secretion actually exist, while 

 the comparison of it with contagia is purely analo- 

 gical ; for the latter are not poisons secreted by 

 glands, but specific organisms ^vhich cause diseases 

 by their multiplication in the animal system. Nei- 

 ther can any confidence be placed in Lacaze- 

 Duthiers' argument deduced from the venoms of 

 different bees or wasps being of different strengths ; 

 for, to say nothing of the fact that the gall-flies 

 belong to a section of the Hymenoptera which uses 

 the ovipositor, not as a weapon of offence or 

 defence as do the bees and wasps, but entirely as 

 an egg-laying instrument; there is undoubted evi- 

 dence that the secretion is not at all of an irritant 

 character. Beyerinck f describes it as tasteless and 

 smell-less, and as a substance which, ^vhen injected 

 under the skin, produces no ill effects, ^vhile the 

 venom of bees or wasps, when introduced in the 

 same way, tends to the same results as if it had 

 been inserted by the insects themselves. x\nd the 

 concurring testimony, based not on hypothesis, but 

 on direct observation of several observers, shows 

 that the use of the secretion is to close up the hole 

 made by the oviiDositor. In another great group of 

 gall-makers— the dipterous family Cecidoinyidce — 

 there can be no question of the poison being the 

 gall-raising agent, for their ovipositors are quite 

 incapable of wounding the plants. 



There is clear evidence, so far at least as the 

 Cynipidce are concerned, that neither the above- 



* An Address on Elementary Patholoyy, delivered before the 

 Medical Congress at Cambridge, 1880. 



t Beyerinck, Beob. il. die ersten Entu'lcklungs'phasen einiger 

 Cynipiden Gallen, p. 186. 



