IffG B. T. L0WNE ON THE HISTOLOGY OF 



The nearest approach to the ordinary muscle fibres of the imago 

 in the insect is the heart muscle of a vertebrate, although the 

 characters of the two arc sufficiently distinct, and the insect muscle 

 is a more elaborately differentiated structure. The physiological 

 character of the ordinary muscles of the imago is not completely 

 understood, and evidence is still desirable on this subject. I 

 believe its contractions are clonic, like those of the heart muscle, 

 rather than tetanic, a sharp, sudden, but not a sustained contrac- 

 tion, and that it is differentiated from other forms of muscle, both 

 morphologically and physiologically. My reason for regarding 

 it as susceptible of powerful single contractions rather than 

 tetanic contraction, is that the muscular movements of the limbs 

 in insects are effected by sudden jerks, which are well seen when 

 the thoracic ganglion is crushed, and the structure of the joints is 

 such that sustained muscular exertion appears to be unneces- 

 sary. The curved mandibles of insects once driven into their 

 prey hold by their mechanical construction, so an insect clings 

 rather by the spinous appendages of the limbs than by sustained 

 muscular power. 



In gold-stained preparations of muscle a network of fibres has 

 been demonstrated,* consisting of very regular transverse networks 

 corresponding to the membranes of Krause, united by fine longi- 

 tudinal fibres ; and it has been recently supposed that the contrac- 

 tion of the muscle is due to the contraction of the longitudinal and 

 its elongation to the contraction of the transverse fibres. If this 

 were the case, the transverse networks being the stronger, the elon- 

 gation of the muscle should be a more powerful act than its con- 

 traction. Possibly the networks are due to the coagulation of the 

 muscle plasma, or they may be an intermuscular nervous plexus, a 

 supposition which has some support from the structure of the 

 electric organs of fishes, and the intern" brillar nervous network of 

 non-striated muscle. 



In conclusion, I would draw attention to a remarkable similarity 

 between muscle fibres and capillary blood-vessels. The myolemma 

 of the former, like the wall of the latter, consists of endothelial 

 plates cemented together, both contain a coagulable fluid, muscle 

 plasma, and blood plasma, and in both there are solid corpuscular 

 bodies, muscle rods in the one, blood corpuscles in the other. The 



* C. F. Marshall, " Quarterly Journal of Microscopic Science," 1887. 



