266 GENERAL ANATOMY OR HISTOLOGY OF BLOiV-FLY. 



regarding it as a direct modification of the cell substance, and 

 not as an excretion formed in the cell and poured out on its 

 surface. I shall hereafter recur to this point. 



The Nucleus. — The appearances presented by nuclei are much 

 more diverse than those exhibited by cells. The nucleus 

 exists in two conditions — the resting stage, which is charac- 

 teristic of a cell which is not undergoing division, and the 

 active nucleus, in the dividing cell. 



The Resting Nucleus in insects is generally enclosed in a 

 thin capsule, and consists of a clear plasma, nucleoplasm, in 

 which a reticulum, or long coil of fibre, is seen; this fibre is 

 termed the nuclear fibre or nuclear skein. It consists of 

 granules, chromatin granules — so called from their affinity for 

 such dyes as logwood or carmine, nuclear stains, when properly 

 applied (see Appendix to Chap. IV.). The chromatin granules 

 are united by a substance which does not stain — achromatin. 



Dkscuhtion of Plate XVI. 

 Cells and Nuclei, exhibiting Iheir principal modifications. 



Fig. I. — A large epithelial cell from the hypoderm of the larva, with striated cell 



substance, a vacuolated nucleus, and a nuclear nucleolus. 

 Fig. 2.- — Two hypodermal cells from the larva in the resting stage. 

 Fig. 3. — Multinucleate pericardial cells from the young nymph, possibly young fat 



cells. 

 Fig. 4. — An amceboid cell from the blood of the young imago, loaded with droplets 



of oil. 

 Fig. 5. — An amoeboid cell from the blood of the young imago. 

 Fig. 6. — An amteboid corpuscle from the same, enclosing a vacuolated nucleus. 

 Fig. 7. — A similar cell with a single droplet of oil in its interior. 

 Fig. 8. — The cell-capsule of an exhausted fat cell from an adult egg-laying female, 



showing stellate daughter cells. 

 Fio. 9. — A young fat cell from the imago. 



Flc. 10. — The nucleus of a fat cell from the nymph filled with leucocytes. 

 Fk;. II. — An epithelial cell from the hypodermis of a larva, showing the intra- 

 cellular reticular spongioplasm ; the nucleus enclosing a nuclear nucleolus. 

 Fig. 12.— The nucleus of a salivary cell from the larva, showing the nuclear thread. 



Fig. 12a. — A portion of the nuclear (chromatin) thread, showing the chromatin 



beads. 

 Fig. 13. — Goblet cells from the proximal intestine of the imago. 

 Fig. 14.— Secretory epithelial cells, from the proximal intestine of the imago. 

 Fig. 15. — Rodded s.ilivary cells from the sericterial glands of the imago. 

 Fig. 16. — Epithelial cell from the distal intestine of the imago, with a stri.aled 



border. 

 Fig. 17. — Large cell from the rectal papilla. 



