Noveiiibfr — December 1S90.] 



PSYCHE. 



411 



In the Wheat louse, SipJionophora 

 avenue Fabr., the third joint is visibly 

 imbricated onlv beyond the middle 

 while all the following joints are ob- 

 viously imbricated. The sensory pits 

 are confined to a single row of eleven, 

 extending from tiie base to beyond the 

 middle of the joint. The 4th joint has 

 no sensory pits and the 5th has a small 

 group near its tip, only. The 6th joint 

 has at the point of greatest dilation, and 

 just before the sudden narrowing, 'a 

 very distinct group of pits, and these 

 are permanent in all stages, and very 

 similar in all species. The absence of 

 these would be a matter of very high 

 systematic value. 



In the Cabbage louse, Aphis brassi- 

 cae Linn., the poriferous system is 

 entirely different. The 3rd joint is not, 

 or but faintly imbricated, while the 

 small, sensory pits are .scattered all over 

 the surface in no regular series and too 

 numerous to count. In a case like 

 this I should expect a considerable 

 range of variation in the number of 

 pits. The 4th joint is imbricated, as 

 are all the following, but has no sensory 

 pits. The 5th joint is very like that of 

 vS. avenue., as is also the 6th. In the 

 immature forms the 5th joint is furnished 

 with a single large pit at tip, and the 

 usual small aggregation on joint 6. 



Fig. 3. 



Fig. 2. 



Aphis cucumeris Forbes, the Melon 

 louse shows a somewhat different type 



