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-fiy, 

 but I think it probable that the dorsal vessel consists of 



Description of Plate XVII. 



The Muscular and Nervous Tissues of the Fly. 



FiC. 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, exhihiting longitudinal stria? and beads due to the 



overlapping of the sarcostyles ; c, a fibril showing the so-called muscle-caset ; /, 



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 ,'j oil immersion lens). 

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



muscle : « h, 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, turn, and a group of parablast cells, />; 



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



muscle cells are fused) ; it, muscle nuclei ; k, nuclei of the muscle-sheath derived 



from the parablast dV oil immersion). 

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



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



the pupa stage (,V oil immersion); j/', 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 {-^ 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 isotropous substance is seen to form 



broad bands between the cells {^^ oil immersion). 

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



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



(iV oil immersion). 

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



vessel attached to its sheath dV oil immersion). 

 Fig. 10.— 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. 



