SECTIONAL TKAN8ACT10NS.— D. 339 



Afternoon. 



Dr. H. W. Miles. — On the Diversity of Habit of three SaufHes (Tenfhre- 

 dinidce) itfestivg Gooseberry. 



The sawflies are Pteronus ribesii Scop., Pt. leucotrochus Htg. and Pristiphora 

 palllpes Lep. ; Pt. ribesii, a multivoltine species, is sharply contrasted with the closely 

 allied P. leucotrochus, a univoltine species. The former oviposits on the undeisurfaces 

 of the leaves, the eggs being inserted on the veins, and the subsequent larvas are more or 

 less gregarious. The latter oviposits on either surface of the leaf, the veins being 

 scarcely ever chosen as oviposition sites ; the eggs are laid singly, and the larva? 

 show little tendency towards gregarious habits. Pristiphora pallipes oviposits within 

 the leaf tissue, and tends to place its eggs singly scattered over the host plant. The 

 larvse feed singly. This species is multivoltine and parthenogenetically thelytokous. 



P. ribesii presents the interesting phenomenon of retarded development in the 

 prepupal stadium, and this tends to modify the usual alternation of sex predominance 

 which is associated with parthenogenesis in species which are arrhenotokoiis. 



Dr. F. A. DiXEY, F.R.S. — Some new points in the development of Insect 

 Wings. 



Mr. J. V. Pearman. — The Natural History of the Psocoptera. 



Short description of Psocids given. 



An attempt has been made to supply a reasonably complete accoimt of psocid life 

 history based on fresh observations and on the few recorded observations. 



It is found that the insects may be grouped roughly in three categories : — (i) 

 surviving representatives of the more primitive stock, (ii) foliage dwellers, and (iii) 

 bark dwellers. 



A particular method of ovipositjon is characteristic of each group. The primitive 

 species deposit their somewhat boat-shaped, sculptured eggs at random ; the foliage 

 dwellers lay groups of smooth, oval eggs and cover them with a sheet of web, while 

 the bark dwellers encase their eggs in a coating of comminuted fragments with or 

 without the further protection of a spun web. With regard to the last mentioned, it 

 is of interest that the chewed particles forming the ensheathing layer are swallowed 

 and pass through the alimentary tract, being deposited in a fluid medium simul- 

 taneously with the egg. 



At hatching the egg shell is cut by a knife-like structure attached to the embryonic 

 cuticle above the head of the larva and controlled by two firm strands of membrane. 

 This oviruptor is operated by the rhythmical depression and inflation of three cephalic 

 ' pulsatory areas.' The embryonic cuticle is shed after partial emergence of the larva. 



In ecdysis, the sloughing of the nymphal integument is a repetition of the process 

 of shedding the embryonic cuticle. There appear to be six pre-imaginal instars. 



Prior to mating the males perform a courtship dance. In pairing the female takes 

 the superior position. 



Food in the majority of cases consists of micro-fungi and algae (principally Pleuro- 

 cocci). Some species devour dead organic matter and a few are entomophagus to 

 some extent and are thus, in a slight degree, of economic value. 



Certain of the more primitive forms have been proved to make a sound by tapping 

 with the abdomen, and in the higher forms structures have been found for which a 

 stridulatory function has been postulated. 



Refekences. 



Pearman, J. V.—' Life Histories ' : Proc. Bristol Xat. Sac, 1927, VI, pt. v, p. 384 ; 

 Ent. Month. Mag., 1927. LXIII, p. 197 ; 1928, LXIV, p. 209, 239, 263 ; 1929, LXV, 

 p. 89. ' Sound Production' : Ent. Month. Mag., 1928, LXIV, p. 179. 



Saturday, September 6. 



Excursion to Dunstcr. 



z2 



