ON THE MOUTH-PARTS IN SOHIZONEURA LANIGERA, 307 



On the Mouth-Parts and Mechanism o£ Suction in ScJiizoneura lanigera, 

 Hausmann. By J. Davidson, M.Sc, F.E.S. (Communicated by 

 Dr. A. D. Imms, F.L.S.) 



(Plates 24 & 25, and 2 Text-figures.) 

 [Read 5tli February, 1914.] 



I. Introductory Bemarks. 



Owing to the great importance of the family Aphididse from the point of 

 view of Economic Entomology, it is thought that a detailed investigation of 

 the structure and mechanism of the mouth-parts and associated structures in 

 a member of this family, may be of considerable help in elucidating many 

 points in connection with the life-history and habits of these insects. 



There are many questions associated with the mechanism of suction in 

 Aphids, about which our knowledge is very obscure. The action of the 

 stylets in the plant tissues is by no means clearly understood, although 

 Biisgen (1890) contributed a great deal to our knowledge of this problem. 



When considering the influence of the sap of certain plants upon the 

 development and reproduction of Aphids, it is very essential to know exactly 

 from which cells the necessary food is derived. There is moreover the 

 question as to why certain species of Aphids produce galls on the host 

 plants, as is the case with the species under consideration. 



From observations made in connection with some experiments I have 

 carried out this summer, it seems evident that these insects are susceptible 

 to changing conditions of growth of the host plant. The present paper has 

 been written in the hope that it may be helpful in the further investigations 

 of the problems mentioned above. It deals only with the anatomy of the 

 mouth-parts and associated structures, and attempts to give a clear account 

 of the way in which the plant juices are conveyed into the pharynx and 

 then passed through the ossophagus into the stomach, and further to explain 

 how the secretion from the salivary glands is forced by the salivary pump 

 into the tissues of the host plant. 



This work has been carried out in the zoological laboratory of the Royal 

 College of Science, London, where the author has been working for the past 

 year as a Board of Agriculture Research Scholar. Through the kindness 

 of Mr. P. Awati, who has been investigating the mouth-parts of Lygus pabu- 

 limis, Linn.^ I have been able to examine his sections, and the comparative 

 observations have been most helpful. Mr. Awati is shortly publishing his 

 paper on Lygus. The reader is referred to a previous paper by the author 

 on the general anatomy of ScJiizoneura lanigera, which gives a more general 

 description of the alimentary canal and associated structures, and should be 

 read in conjunction with this paper. 



LINN. JOURN. ZOOLOGY, VOL. XXXII. ■ ^ — 7^17T-^^ 



