42 A. KEIJNE, A COCOONSPINNING THRIPS. 



to prepupa they are cast and it is very difficult to trace the 

 new ones in the pupa and prepupa. When the pupa molts, 

 their appearance is again very distinct and the insect again 

 starts feeding. In the pupae of F. tciiuicoriiis also no distinct 

 inouthspines are seen, whilst those in the larvae and the 

 cast larval skins are ver)' conspicuous b}' their strong 

 chitinization. 



Besides the presence of onl}' one cast skin within the 

 cocoon of the pupa, which apparently is the larval skin, the 

 following observation also proves, that probably no prepupa- 

 stage exists. One larva, that started spinning at ii°° a.m., 

 was still larva the next day at /"" a. m., but another, that 

 began at 8'5 a. m., was a pupa on the next day at 73° a.m., 

 the difference onl)' being 3 hours 15 minutes. That the 

 prepupa-stage is sometimes omitted, was proved b)' another 

 observation on the cacaothrips A larva was put on a hollow 

 objectslide, closed by a coverglass, for the purpose of drawing 

 it; meanwhile it molted and a complete pupa emerged. 



During spinning the head and fore-legs are ver)' active, 

 but not the abdomen ; this is clearly visible when the larva 

 is seen suspended from the upper wall of the cocoon. The 

 fore-legs easih' ph' in the tibio-femur articulation. I could 

 not find any trace of glands in these legs, so that the spun 

 threads are probably produced b)' the mouth, but as the 

 head is moved very quickly, this could not be seen under the 

 microscope. The long slender antennae are bent backward 

 and pressed against the wall of the web; they may possibly 

 render some service in giving the cocoon its right shape 

 and dimensions. The cocoon itself consists of anastomosing 

 threads of variable thickness, somewhat thickened at the 

 knots (fig. 5). 



Generally the pupa seems to spin no more, but the 

 following observation indicates, that it may be able to do 

 so. A hole was found in the cocoon of a pupa that had 

 been spun one day before and was uninjured in three former 

 observations; 15 hours later it was again closed. 



Once it was seen, that a larva, just begun with spinning, 

 broke its silk, which seemed to require a great effort, though 

 there were onl)' very few threads (fig. 4). How this is done 



