172 



HARDWICKE'S SCIENCE-GOSSIP. 



with the troplii are as follows; viz.— 1st, three 

 small pairs, which arise from the upper internal 

 surface of the head, and are inserted into the com- 

 mencement of the oesophagus on its upper surface, 

 and between which the nerves to be hereafter 



Fig. 107. General plan of the muscular and respiratory 

 systems, showing 1 , en the left hand at m m, the successive 

 series of longitudinal, diagonal; and transverse muscles, 

 and at //, one of the looping mu'clei connecting the seventh, 

 eighth, and ninth segments. In the centre is seen the 

 ventral cord, and on the right hand one of the main trachea: 

 t t, together with its subsidiary trunk V t y . At s s are the 

 spiracles, at r r the offsets to the viscera, at g g those to the 

 ganglia of the cord, slightly magnified. 



described, which connect the frontal sympathetic 

 ganglion with the brain, pass ; 2nd, a pair of 

 muscles which arise one on each side of the central 

 internal ridge of the spur, and are also inserted into 

 the upper surface of the oesophagus, shortly above 

 the point where it passes through the brain. Be- 

 tween these muscles lies the funnel-shaped orifice of 

 the dorsal vessel. I am inclined to think that the 

 office of these muscles is in some way to control the 

 supply of the circulating fluid through the latter 

 organ ; 3rd, another pair of muscles also arise from 

 the back of the head, and appear to be inserted on 



the upper surface of the salivary duct, immediately 

 below its commencement. I suspect these are the 

 homologues of the pair of muscles mentioned by 

 Mr. Lowne, as opening the valve of the salivary 

 duct of the Blow-fly.* Between these I have some- 



Fig. 108. /, Longitudinal vertical section of the head, a little 

 to one side of the central line, showii g the great flexor 

 muscles of the mandibles, slightly magnified, e, Ditto 

 further removed from the centre, showing the extensor 

 muscles of the mandibles and those connected with the 

 maxilla?, s, Transverse vertical section ot the same, show- 

 ing the oesophagus, the processes of the mandibles with the 

 flexor muscles attached, and externally to these the extensor 

 muscles. 



times seen membranous curtains, with a free poste- 

 rior edge. 



The muscles of the body consist of flat bands or 

 strips, varying from ^iv to ^ of an inch across, 

 each inclosed in a transparent membranous sheath, 



Oy 



o ° c 



Fig. 109. a. Portions of two contiguous sets of muscles, show- 

 ing their manner of junction, x 50. h, Portion of muscle 

 undergoing destructive change x 120. c d e. Result of 

 this change ; c, as usually seen after the insect has been 

 preserved in spirit ; d, after treatment with liquor potassie ; 

 e, in groups, x 350. 



or myolemma."* It would thus appear that each 

 strip must be regarded as a separate muscular 

 fibre ; they differ, however, from all other examples 

 of muscular fibre with which I am acquainted, 

 firstly, in their great size, and secondly in the fact 

 that each fibre seems to form a separate and inde- 

 pendent muscle. 



* Lowne's " Anatomy of the Blow-fly," p. 52. 



