METHOD OF DISSECTING FLEAS 473 



composed of two lateral halves. This primitive condition of the nervous 

 system is a strong argument against fleas having had winged ancestors. 

 They are not degraded Diptera. 



DISSECTION 



While it is a matter of very great difficulty to make a complete 

 dissection of any of the systems of the flea, it is comparatively easy to 

 get out any one organ for examination. The one point which it is 

 absolutely essential to attend to before one can have any hope of success 

 is to see that the needles are sharp. The integument of the flea is a 

 very tough one, and some parts of it are extremely hard to cut steadily. 

 Before commencing the dissection the legs should be cut off or pulled off 

 near the body, if possible tearing out the coxae. 



The mid-gut may be obtained by the following method. Place a 

 blunt needle firmly on the thorax, holding it rather flat. If the flea 

 cannot be steadied in this way insert the point of the 



needle between the head and the prothorax, just at Dl88ectlon of the 



mid-gut 



or behind the pronotal comb if there is one. Keeping 



this needle steady, place the other, which should be very sharp, on 

 the first segment of the abdomen, and press it slowly down towards 

 the slide. The point will not at first pierce the integument, but 

 will slip to one side, and by gradually increasing the pressure as the 

 margin is approached one can nip a piece of either the dorsal or 

 the ventral margin between the point and the glass. It is best to 

 take the dorsal margin. Now pull gently, keeping a firm grip with 

 both needles. The abdominal tergite will then separate from its 

 attachment to the metathorax at the dorsal angle. When once the 

 separation has begun it can be increased by putting both needles in 

 the fissure and widening it. Next cut the last segment of the abdomen 

 away from the body with a sharp blade-like needle, so as to loosen the 

 posterior attachment of the gut. When this has been done place one 

 needle on the last remaining segment and one on the head or prothorax, 

 and pull gently. The proventriculus and mid-gut will come out of the 

 abdomen and will remain attached to the head by means of the fine 

 oesophagus. They can then be easily separated and removed to another 

 slide. 



The hind-gut is comparatively easy to remove ; it lies coiled up at the 

 posterior end of the body, so that one can safely begin by cutting across 



the anterior portion of the abdomen, probably severing 



. . The hind-gut 



the mid-gut. Then by stroking the remaining portion 



60 



