GENERAL STRUCTURE. 



41 



enabling the drone to contract the abdomen so as 

 to produce the expulsive act. One of these fibres, 

 where shortened and thickened (as at a, Fig. 9), 

 may measure ^Joth °f an ^ ncn in diameter, while 

 the relaxed portion of the fibre is about T ^ n - ^ 

 this muscle be skilfully and quickly removed, and 

 placed either in the fluids of the animal or in a 

 little weak salt and water, upon the microscope 



Fig. 9.— Muscular Fibres of Drone (Magnified 300 Times). 

 a, Part of Fibre, contracted; b, Part relaxed ; tr, Trachea; n, Nerve. 



stage, the wave of contraction may be seen play- 

 ing along the fibre, almost as one observes it 

 in a garden worm, as it draws up the hinder part 

 of the body whilst moving onwards. The part 

 (as at b) quickly, by bringing together its plates, 

 assumes the appearance of a, while a extends itself, 

 plate by plate, until it is fully relaxed. The contrac- 

 tion soon ceases, but I have watched it in operation 

 for at least two minutes. Nerves (n, Fig. 9) 



