F. R. Petherbridge and M. A. Husain 183 



difficulties encountered we were able to carry through to the adult stage 

 three individuals of P. rugicollis which hatched in the laboratory. From 

 the cage cases we got a complete record of the times of moulting and 

 the duration of each instar which on comparison proved very similar to 

 those under normal conditions at Wisbech. All doubtful cases were 

 discarded and the figures given in Table II (p. 192) are those about which 

 there is no doubt. 



The records of the life-history in the cages in the laboratory were 

 compared with the sleeve cases at the farm and with those under normal 

 conditions at Wisbech and were found to agree closely, in the laboratory 

 the hatching and certain moults were in some cases a day or so ahead. 

 We failed to fuid P. rugicollis copulating in spite of the fact that we put 

 males and females together on shoots in the cages. We tried to watch 

 the process of egg laying, but in spite of careful watcliing we were 

 unsuccessful. For this purpose we had lengths of glass tubing about one 

 inch in diameter, closed at one end by a piece of muslin and at the other 

 by a cork with a hole in it. An apple twig with a $ P. rugicollis on it 

 was introduced in the tube and the end put through the hole in the cork; 

 the basal end of the twig being outside was placed in water and so kept 

 fresh. A later examination of these twigs showed that eggs had been laid. 

 Some of these twigs with eggs were dissected and photographed. 



During the early part of the experiment shoots of Bramley's Seedling, 

 Early Victoria (Emneth Early), Grenadier, Keswick Codling, Lord Gros- 

 venor and Worcester Pearmain were used in the cages, but later on, 

 owing to the difficulty of getting twigs, we had no time to find out the 

 varieties used. 



P. rugicollis caused characteristic markings in every case. Details 

 of these markings are given under the description of the injury done by 

 this species. 



Psallus ambiguus, Orthotylus marginalis and Atraciotomus mali were at 

 first put on shoots of Keswick Codling and Bramley's Seedling and later 

 on several other varieties, but as far as we could see they did not change 

 the appearance of the leaf or fruit and certainly did not cause any mark- 

 ings of a similar nature to those caused by P. rugicollis. 



The drawings were done by means of a camera lucida. 



A large number of measurements of the different parts are given as 

 the length of a larva or nymph is very variable according to its food 

 supply, a well-fed larva being much longer than a starved individual as 

 in the latter ^he basal joints of the abdomen become telescoped. Owing 

 to this we subdivided P. rugicollis into A and B and expected to get two 



