268 GENERAL AXAIOMY OR HISTOLOGY OF BLOW-FLY. 



that he had observed the same thing in Musca. Eimer* has 

 recorded the appearance of the non-stained thread uniting the 

 chromatin granules. 



Carnoy [129] describes the nuclear thread of insects as com- 

 posed of numerous minute chromatin granules, united by a 

 clear material, and states that they sometimes surround a central 

 cavity, or, in exceptional cases, form a spiral fibre. I have 

 never seen these appearances, and this is the more remarkable 

 as Carnoy describes them as occurring in the hypodermis of the 

 Blow-fly larva. My failure to do so is probably due to a different 

 method of preparation. When fresh nuclei are examined in 

 Flemming's mixture, or even in normal saline solution.f I have 

 repeatedly seen the nuclear threads divided into transparent 

 discs, which remind me of rouleaux of human blood corpuscles, 

 except that they are smaller and colourless. They are highly 

 refractive. 



It is a fact worthy of note that, although the nuclear skein is 

 so well developed in the large nuclei of the salivary cells, 

 the fat bodies, and the epidermis, these cells never undergo 

 division, and are destined to be completely destroyed by the 

 action of phagocytes in the first days of the pupa stage (see 

 Chap. IX.). 



Nucleoli. — It frequently happens that one or two larger, 

 highly-refractive masses are seen suspended in the nucleoplasm ; 

 these are termed nucleoli. Some regard them as mere isolated 

 masses of chromatin ; others, as distinct in nature and chemical 

 composition. 



I am inclined to think that the history of nucleoli has yet to 

 be written. Some are undoubtedly merely the remains of a 

 degenerated or degenerating nuclear thread. Such masses are 

 sometimes comparatively large and irregular in form ; they are 

 seen in numbers in the degenerated tissues of the pronymph. 

 Others, which are distinguished by Carnoy as nuclear nucleoli, 

 resemble a minute nucleus, and have granules of chromatin in 



* Eimer, ' Ueber den Bau des Zellenkerns,' Archiv f. mik. Anat., 

 Bd. xiv. 



t X o"65 solution of common salt. 



