561 



DISSECTION 



The internal organs of lice cannot be dissected out by the methods 

 which succeed in the case of the Diptera, owing to the tough nature of 

 the integument and to the close union between the segments of the exo- 

 skeleton. The integument cannot be torn, and there are no weak places 

 between the segments at which it can be easily incised. It is therefore 

 necessary to adopt other procedure. 



The following method has been found successful. Cut off the legs as 

 near their junction with the thorax as possible, using a pair of fine 

 scissors, or remove them by cutting through the 



joint between the coxa and femur with a sharp needle. Ex P* ure of lnternal 



Organs 



Remove them from the slide, and lay the louse on its 



dorsal surface with the head away from the observer, and steady the 

 anterior end with a needle held flat on the thorax or between the thorax 

 and the head. Then take a sharp lancet-like needle and cut off, with one 

 incision if possible, the whole of the lateral margin internal to the 

 stigmata, from the anterior to the posterior end. When this has been 

 done some of the organs, probably the ovaries if they are mature, will 

 slip out through the gap. Then turn the insect round the other way 

 and repeat the manoeuvre on the other side, so that the dorsal and ventral 

 surfaces of the integument are separated from one another except at the 

 anterior and posterior ends. Next thrust a needle under the ventral part 

 of the skin from side to side and, using it as a director, cut transversely 

 across the ventral flap about its middle ; the transverse cut is made most 

 easily if the louse is turned over on its ventral surface after the director 

 has been inserted. The two flaps can then be easily dissected forwards 

 and backwards by severing the tracheae attached to them, and in the 

 case of the larger lice they can be cut off with scissors and removed. 

 The internal organs are now exposed. 



The genital organs lie ventral to the gut, and should be removed first. 

 In the case of the male the long cylindrical receptacula will be recognized 



at once by their characteristic shape and contour. 



* Removal of the Re- 



Pull these forwards and stretch them a little, and the productive Organs 



ejaculatory duct, passing to the penis, will be seen. 

 This should be cut across with a needle, and the whole system removed. 

 The testes are placed far forwards in the abdomen and are surrounded 

 by a mass of fat body ; if they are not required for examination the vasa 

 can be cut across and the testes allowed to remain in situ. In the 

 female the ovaries lie on either side of the gut, but their attachments are 

 71 



