284 GENERAL ANATOMY OR HISTOLOGY OF BLOW-FLY.'; .\ 



whole tube. Nuclei are seen at very regular intervals, one on 

 either side of the dorsal vessel. According to Viallanes [27], 

 it consists in Eristalis of a series of segments, each containing 

 a pair of nuclei, one on either side. The segments are united 

 by fine lines of cement material, which is stained by nitrate of 

 silver. I have been unable to obtain definite results with 

 silver nitrate either in the larva or imago of the Blow-fly, 

 but I think it probable that the dorsal vessel consists of 



Description of Plate XVII. 

 The Muscular and Nervous Tissues of the Fly. 



Fig. I. — Sarcostyles : a, from the ordinary muscles ; b, the same when stretched; 



c, appearances due to the overlapping of the sarcostyles when stretched ; d, a 



portion of a muscle fibril, exhilnting longitudinal striae and beads due to the 



overlapping of the sarcostyles ; e, a fibril showing the so-called muscle-cases ; f, 



sarcostyle from one of the great thoracic (wing) muscles ; g, another sarcostyle 



from the same, showing a granular appearance, probably due to post-mortem 



change (all seen with a yV oil immersion lens). 

 Fig. 2. — A transverse section of a pprtion of one of the fasciculi of the great dorsal 



muscle : ;/ n, nerve fibres ending in the muscle. 

 Fig. 3. — A longitudinal section of a fasciculus of the same. 

 Fig. 4. — Two stages in the development of the great dorsal muscle : a, an early stage, 



showing two rows of muscle cells, ww, and a group of parablast cells, p ; 



b, a later stage, in which the fibrillation of the muscle has commenced (ihe 



muscle cells are fused) ; ;/, muscle nuclei ; /•, nuclei of the muscle-sheath derived 



from the parablast (j^ oil immersion). 

 Fig. 5. — Tendon-like terminations of the muscles : j«, connective reticulum between 



the tergum and the young dorsalis muscle, from a nymph on the fourth day of 



the pupa stage (yV oil immersion) ; jb, tendon-like insertion of an ordinary 



muscle from an immature imago. 

 Fig. 6. — Transverse sections of ordinary muscle fibres near their insertion into the 



integument, showing a concentric arrangement of the muscle substance (^V oil 



immersion). 

 Fig. 7. — Karyokinetic figures and cell-plates in an ordinary muscle fibre, from a nymph 



on the twelfth day of the pupa state. The is<Hropous substance is seen to form 



broad bands between the cells (yV oil immersion). 

 Fig. 8. — a. Transverse sectioris of ordinary muscle fibres of the adult imago, showing 



nerve-terminals ; b, a more highly magnified representation of the nerve-terminal 



(yV oil immersion). 

 Fig. 9.^A transverse section of the labial nerve of the proboscis, with a tracheal 



vessel attached to its sheath (y'^ oil immersion). 

 Fig. id. — A similar nerve seen in the longitudinal section, showing the ganglion cells. 

 Fig. II. — A ganglion cell from the thoracic ganglion. 

 Fig. 12. — Two small ganglion cells from the optic ganglion. 



Fig. 13. — A sensory seta showing the trichogenic and ganglion cells at its base. A 

 process from the ganglion cell apparently ends in the nucleus of the trichogenic 



cell. 



