38 THE MAGGOT OP THE BLOW-FLY. 



the nervous mass is sub-oesophageal, and probably consists of 

 twelve ganglia blended together, one for each segment. From 

 this, nerves, accompanied by tracheae, are given off to the various 

 parts of the body. The nerve-centres are surrounded by the 

 growing imaginal discs, from which the limbs of the fly are deve- 

 loped. I have not been able to work them out fully. They are, 

 however, well described in Mr. Lowne's book, and consist of 

 cellular expansions attached to the nerves and tracheae. 



Much of the structure of this maggot may be seen by simply 

 compressing it in a live box or compressorium, and viewing with a 

 low power. If it be placed in a little water in a watch-glass, under 

 a lens, and cut in half, the viscera will be immediately extruded, 

 and with the aid of one or two needles may be placed for 

 examination under the microscope, when nearly all I have 

 described may be seen. 



EXPLANATION OF PLATE XX. 



Fig. 1. — Organs of Maggot seen sideways: jA, pharynx ; c, crop ; j)., 

 proventriculus ; i. , convolutions of intestine. 



Fig. 2, — Epithelial cells of integument as seen under a j-inch objective. 



Fig. 3. — Diagram showing relations of inner and outer coats of integu- 

 ment : c. , outer cuticular layer ; e. , epithelium ; a,c. , alimen- 

 tary canal. 



Fig. 4. — Alimentary canal : ce. , oesophagus ; c. , crop ; n., nerve-centres ; 

 p., proventriculus; cob. , cseca; ij. , ventriculus ; ■i., intestine ; 

 a., anus ; b.t.,h.t.y bile-tubes. The salivary glands are shown 

 separately. 



Fig. 5. — The salivary glands. 



Fig. 6.— Bile tube. 



Fig. 7. — Pharynx, front view: p.p. p.p., processes; ce. , oesophagus; 

 m.d, m.d.y mandibles; s.d., salivary duct; m.m.f muscles 

 of mandibles. 



Fig. 8. — Ditto from the side, letters as before. 



Fig. 9. — Transverse section of ditto; m.m., muscles. 



Fig. 10.— Cells of fatty rete. 



Fig. 11. — Tracheal system. 



Fig. 12. — Portion of trachea, showing coats. 



Fig. 13. — Posterior spiracle. 



Fig. 14.— Anterior ditto. 



