118 PRACTICAL HISTOLOGY. 



for the purpose is the common great water-beetle 

 (Dytiscus marginalis), and the muscles of the limbs, 

 especially the forelegs of the males, 1 which are strong 

 and well-developed, should be chosen. A slide and 

 cover-glass having been cleaned, and a lance-pointed 

 needle or a scalpel and fine scissors and forceps being 

 at hand, one of these limbs is cut off at the joint 

 nearest the body, wiped with blotting-paper to free 

 it from the acrid, strongly-smelling secretion which 

 the insect emits, and the chitinous integument of the 

 limb is then slit longitudinally so as to expose the 

 pale soft-looking muscle within. Then, the member 

 being firmly held on to the table with forceps or the 

 fingers, as much as possible of this muscular tissue 

 is gouged out with the lance-headed needle or scalpel- 

 point, and transferred to the slide. The muscular 

 fibres are quickly separated somewhat from one 

 another by needles, desiccation being prevented by 

 breathing once or twice upon the preparation, and 

 the cover-glass is immediately laid on without the 

 addition of any fluid other than that which naturally 

 moistens the tissue. The preparation is to be ex- 

 amined at once with the highest available power. 

 It is difficult to make out the details of the structure 

 with a combination magnifying less than 1000 dia- 

 meters, and the defining power must be of the best. 

 If the object has been quickly enough prepared, 

 numerous fibres will be found which show the suc- 

 cessive series of minute muscle-rods, corresponding 

 in position with the darker cross stripes of the mus- 

 cle, and prolonged into the clear stripes, where they 

 end with knobbed extremities, the juxtaposition of 

 Avhich in rows side by side gives the semblance of a 

 dotted line in each clear stripe, single or double accord- 

 ing as the fibre is more or less extended. Other fibres 



1 The males are readily distinguished from the femnles by their 

 smooth wing-covers, whereas those of the females are rigid and 

 furrowed longitudinally, as well as by their short strong fore- 

 limbs with sucker-like extremities. 



