iv] INTERNAL ORGANS OF A FLEA 61 



The internal organs of fleas cannot be studied 

 without dissection under a microscope. Dissection 

 is best carried on in a solution of salt and water. 

 Fine needles mounted in penholders are the most 

 handy implements. But the point of even the finest 

 commercial needle that can be bought is too blunt 

 for fine dissections, and it is necessary to sharpen it. 

 This can be done by the help of a rapidly revolving 

 emery wheel, varying the inclination of the needle- 

 point to the wheel, so as to grind off the angles. The 

 flea to be dissected is put in a drop of salt solution, 

 on a slide placed on the stage of the dissecting micro- 

 scope. In the left hand should be a needle with a 

 blunt conical point, in the right a needle with an 

 oblique point. The antennary groove of the flea 

 should then be transfixed and held firmly by the 

 left-hand needle. 



The point of the right-hand needle is then inserted 

 under the edge of the third or fourth abdominal seg- 

 ments. The segments can then be peeled off by a 

 skilful dissector much as we peel off the skin of a 

 shrimp for our tea at the sea-side. The internal 

 organs of the flea then float off in the salt solution ; 

 and by using two very fine pointed needles they can 

 be further separated. It is useful to have one needle 

 ready with a hooked end and another fashioned into 

 a minute knife or scalpel. 



The most conspicuous of the internal organs will 



