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Mr. J. B. Hay craft. Upon the Cause of [Feb. 3, 



point more difficult to decide perhaps than in the case of the skeletal 

 muscles. Transverse cleavage takes place here also in the thinner 

 part of the fibre, namely, in the bright stripe, but whether or not 

 exactly in Dobie's line I have not yet definitely made out. 



A curious appearance often presented by insects' muscle, and some- 

 times also by that of the mammalia, has been described and figured by 

 Mr. Schafer. A paper descriptive of these he communicated to the 

 Royal Society of London (1873), which came out later on in the 

 " Transactions " of this Society, and his observations are published 

 also in the eighth edition of Quain's " Anatomy." These have been 

 almost entirely overlooked by French and German physiologists, yet 

 in many English laboratories his observations have been verified, and 

 his conclusions taught. 



They are well illustrated in a representation of the muscular fibre 

 of a Dytiscus, which may be seen in Quain's " Anatomy." The dark 

 stripes are traversed longitudinally by dark rods, which end at both 

 extremities in little knobs. These knobs lie in the borderland between 

 the bright and dark stripes. The only point which I would add to 

 his figure is this, that the knobs are joined across the clear stripes or 

 valleys by lines, just as they are so joined across the dark stripes, 

 although the lens must be depressed ever so little to make this out. 

 These lines are, in fact, nothing more or less than the longitudinal 

 strise described many years ago as lying between the fibriHae of which 

 the fibre is composed, these little knobs lying in their course. This 

 can, perhaps, most conclusively be made out in the following way. 

 Allow a piece of insect's muscle to remain in a drop of water for some 

 hours (which will vary with the temperature) until it has partially 

 putrefied. Then cover and examine, when many of the fibres will 

 have separated towards their ends into fibrilke. One can then dis- 

 tinctly trace the chinks between the separated fibrillas as being con- 

 tinuous with the striee, on which the knobs are still seen, in the centre 

 of the fibre. I think that the following is a feasible explanation of 

 these knob-like enlargements of the cementing substance seen as 

 longitudinal stria?. These knobs occur, as will be beautifully seen on 

 referring to the woodcut in Quain, on the slopes between the valleys 

 and the ridges. The cementing substance dips down here with the 

 fibre itself, and if there be the slightest lateral obliquity it will appear 

 larger. The cementing matter is seen on edge, and differing as it 

 does from the muscle-substance in refrangibility, a distortion occurs, 

 giving rise not to a dark line as on the surface, but to a dark knob. 

 This is, in fact, but an optical delusion, for the striee are quite 

 uniform, and were the fibre cylindrical would appear so. This may 

 be proved by the fact that very often if the rays of light from the 

 reflector are oblique, but one set of dots appears, which shift over to 

 the other side on twisting the mirror. By shifting the preparation 



