254 Some Observations on the Egg of Psylla mali 



sap in the vicinity of the process would cause an equally sudden increase 

 of pressure inside the egg which might be just enough to cause hatching 

 if the larva were in an advanced enough state. 



The middle membrane. This is thin and is apparently not chitinous 

 as picric acid does not stain it. It has no sculpturings like the outer 

 membrane. It possesses a hollow thin-walled process which follows 

 the position of the outer membrane process, reaching in the norma] 



outer membrane 

 middle 



, hollow process 



of 

 middle membrane 



ditto of outer 



bark of twig 



Fig. 1. Outline of egg membranes and processes. 



..-s -outer membrane 



solid process 

 Fig. 2. Outer membrane. 



■outer membrane 

 ■-middle ,, 



Fig. 3. Hollow prooess 



(highly magnified). 



position about two-thirds way down it (Fig. 3). On treatment with 

 reagents some contraction usually takes place so that it may be partially 

 withdrawn (Fig. 1). 



The inner membrane This is extremely thin and is easily destroyed 

 when preparing specimens, so that unless some care is exercised it 

 cannot be seen. It has no process, but at the anterior end are two 

 tubercles and a peculiar modified area (Figs. 1, 4, 5). The larger 

 (Fig. 6 A) LS doisallv situated and doubtless is the chief agent used 



