In vitellogenic oocytes of Tenebrio molitor (inactive stage), numerous 
fibrogranular nuclear bodies (NBs) are present. Using immunofluorescent 
microscopy, these NBs were shown to contain pre-mRNA splicing factors (small 
nuclear [sn] RNPs and SR-protein, SC35) as well as RNA polymerase II. A limited 
set of NBs also contained coilin, a marker protein for Cajal bodies (CBs). We 
suggest that in T. molitor oocytes, coilin-containing NBs, which also contain 
splicing factors and RNA polymerase II, seem to represent CBs. In the species 
studied, no morphological features of CBs were established as compared with 
other NBs, which do not contain coilin. Microinjectons in oocytes of myc-tagged 
coilin mRNA, followed by revealing newly translated protein with antibody 
specific for this tag, have shown targeting of myc-coilin with CBs. The own and 
literary data on the morphology and molecular composition of CBs are discussed 
in terms of searching for criteria for CB identification in cells of different 
origin, and at active and inactive stages.