36 MEDICAL ENTOMOLOGY 



and much of the alimentary canal. The sting can be recognized 

 at once as a fine needle-like structure, and the venom sac as a 

 very small semi-transparent sac. With needles carefully sepa- 

 rate the sting with the sac and other accessory structures. 

 Teasing out these structures can well be accomplished under 

 water, with the aid of a dissecting microscope or binocular. The 

 following parts should be noted, drawn and labelled: 



a. The sting proper, consisting of two darts, ending in distinct 

 serrations and bending at the base to either side for muscular 

 attachment and leverage. 



b. The sheath, partly enclosing the upper part of the darts, 

 and terminating in a fine cutting edge at the distal edge of the 

 sting proper. It also serves to direct the flow of venom into the 

 wound. 



c. The sting palpi, situated on either side of the darts. 



d. The venom sac, emptying by means of a broad neck into 

 the poison channel. 



e. The poison gland, recognizable as a long coiled tube leading 

 into the anterior end of the venom sac. 



EXERCISE 21b 



VENOMOUS SPIDERS AND SCORPIONS 

 CLASS ARACHNIDA, ORDER ARANEIDA AND ORDER SCORPIONIDA 



A. The most venomous of our few dangerous spiders is Lac- 

 trodectes mactans. With a specimen of this spider before you, 

 note the following characteristics: 



a. It is a medium-sized spider. 



b. The color is brownish black to inky black. 



c. Notice two brick red triangular spots on ventral side of 

 abdomen. 



