163 



proves to be Aspidiotus dictyospermi Morg., a species often 

 found on a considérable variety of greenhouse plants, no- 

 tably on palms. It is also common in tropical countries, 

 and has a Worldwide distribution, out of doors in the 

 tropics, and in hothouses in temperate countries." 



On this place I wish to express my thankfulness to 

 Professer Cockerell for liis friendly médiation and to 

 the entomologists of the U. S. Department of Agriculture 

 in Washington for their determining of the Coccid. 



That suspicion fell on this Aspidiotus had a very simple 

 reason. 



Although not nearly ail the leaves, showing yellow 

 vesicles, still carried scale-insects, yet the reverse was 

 generally true and it soon became apparent that the leaves, 

 carrying scale-insects generally also had some yellow 

 vesicles. 



But unexpected difflculties were experienced when it 

 was attempted by means of microtome préparations to 

 obtain certainty and a clearer insight in what had been 

 rendered probable by macroscopical observation. A great 

 difficulty was that the majority of the insects refused to 

 stick to the bits of leaf from which the microtome pré- 

 parations were going to be made. While a great part 

 already let loose during the treatment, preceding the em- 

 bedding itself, their example was followed by most others 

 when they were put into the melted paraffin. It was 

 supposed that perhaps the reason of this was that the 

 scale-insects, when coming into the flxing solution, with- 

 drew their suction organ from the tissue of the leaf, pos- 

 sibly on account of a pre-mortal reactional movement. 

 After this unfavourable resuit the leaves carrying the 

 insects were always treated before fixation with an anaes- 

 thetic, namely aether. This précaution, however, did not 

 materially improve the results. 



Among the microtome préparations which I obtained in 



