580 HEMIPTERA-HOMOPTERA CHAP. 



from the sides of the body, so that the width of the creature is about 

 as great as the length. The period occupied by the development 

 apparently varies according to season. Witlaczil, who has given an 

 account of many details of the anatomy and histology of various 

 Psyllidae, 1 considers that there are four larval stages ; Heeger's 

 account of Psylla succincta is not quite clear on this point, and 

 Slingerland indicates a stage more than this, the perfect Insect 

 being disclosed as the result of a fifth moult ; it is probable that he is 

 correct. In these earlier stages the body bears long hairs called 

 wax-hairs ; according to Witlaczil in the young larvae of certain 

 species Trioza rJiamni, e.g. these are broad and flat, so as to 

 make the body appear studded with oval processes ; he states 

 that these hairs change their form during the growth of the 

 individual. Nothing is more remarkable in Psyllidae than the 

 amount of matter they secrete or exude from their bodies ; in 

 some species the substance is a " honey- dew," and the nymph 

 may keep itself covered with a drop of it : in other cases it is 

 solid, as shown in Reaumur's figures of P. ~buxi, where this exuda- 

 tion forms a string several times longer than the body, and attached 

 to it. Another form of exudation is a light downy or waxy 

 matter. Slingerland says that honey-dew was exuded by P. 

 pyricola in such quantities that it " literally rained from the trees 

 upon the vegetation beneath ; in cultivating the orchard the back 

 of the horse and the harness often became covered with the 

 sticky substance dropping from the trees. It attracts thousands 

 of ants, bees, and wasps, which feed upon it." The writer last 

 year observed in the New Forest a stunted sloe-bush, about which 

 a large number of Bombi were busily occupied ; and examination 

 showed that they were thrusting their proboscides into the curled 

 and deformed leaves, in which were secreted nymphs of a Psylla 

 exuding honey-dew. It must not be assumed that this honey- 

 dew is the excrement of the Insect ; this also is known, and is a 

 different substance. Those who have tasted it say that the 

 honey-dew has a clean, good flavour. The source of the honey- 

 dew is not quite certain, but it seems probable that it comes, like 

 the solid matter figured by Eeaumur, directly from the alimentary 

 canal, and not from hairs or pores on the body. Psyllidae give 

 rise to definite formations or galls on certain plants ; sometimes 

 these Psyllid galls are mere changes in form of a limited part, or 



1 Zeitschr. wiss. Zool. xlii. 1885, pp. 569-638. 



