K. Hargreaves :\'2i) 



Parthenogenesis. I placed three females, isolated before complete 

 emergence so as to be absolutely certain that they had not been fertilised, 

 each on a clean plant. From these I obtained ten, thirteen and twenty 

 imagos respectively, all females. From these I got females again, and 

 out of the hundreds of flies which I examined I did not encounter a 

 single male. 



Morrill^ on parthenogenesis in the Aleyrodidae, states that un- 

 fertilised eggs hatch giving larvae which result in male flies, and suggests 

 that the fertilised eggs will all give rise to females, as in bees. Morrill 

 and Back further established parthenogenesis in Alei/rodes citri. 



Some General Notes. 



Spiracles. There is evidence for the presence of three pairs of 

 abdominal spiracles in the first three instars. In the other two, however, 

 there is not. It might be suggested that this reduction during develop- 

 ment is some indication that an ancestor of the Aleyrodidae had a pair 

 of spiracles in each abdominal segment. These may possibly be 

 developed in the embryo, all except the remaining three being absorbed 

 before hatching. 



Breathing folds. In the case of the instars which are fixed in one 

 place during their existence, viz. the second, third and fourth, they are 

 fixed to the leaf by the waxy fringe. Since the spiracles are ventral, 

 there must be some arrangement for the access of air. This requirement 

 is met by the "breathing folds." On each side of the thorax, opposite 

 the first pair of thoracic spiracles, the ventral body-wall is transversely 

 folded, the fold being continued along the sides of the thorax and part 

 of the abdomen. This allows for the access of air to the thoracic and 

 first abdominal spiracles. The animal forms a floor of wax to these folds, 

 thus converting them into tubes (Fig. 33). The margin at the openings 

 of these difters from the rest (Figs. 34, 35). There is a similar median 

 longitudinal one posteriorly for the access of air to the spiracles on the 

 sides of the vasiform orifice. In the first larva, either the folds are absent, 

 or are too small for observation. But there may be other arrange- 

 ments in this case, if such are required. In the first place, I have seen 

 a few of the larvae walking about after the formation of the waxy 

 fringe, which suggests that the fringe is not in contact with the leaf. 

 This would obviate the necessity of breathing folds. Also, there is a 

 long spine on the inside of the basal joint of each leg, and a pair of long 

 ones beneath the vasiform orifice. These may function as resting 



