44 ARTHROPODS 



Internal Structure. — (i) Pin the caterpillar ven- 

 tral side down, in a dissecting tray, by placing a pin just 

 behind the head and another through the last segment 

 of the abdomen. Make an incision on each side about 

 midway between the rows of spiracles and the mid-dorsal 

 line. Raise this dorsal strip, being careful not to injure 

 the parts beneath, and cut it of?. 



(2) This exposes the transverse muscles. What motion 

 do these muscles produce? 



(3) Just beneath the transverse muscles find the longi- 

 tudinal muscles of the dorsal side. Contraction of these 

 muscles produces what motion? 



(4) Separate the above muscles ; find beneath a whitish, 

 stringlike organ, the heart. Trace it from anterior to pos- 

 terior end. 



(5) On either side of and below the heart, extending 

 from the posterior end of the body to the thorax find the 

 delicate, yellowish-white coiled tubes, uriniferous or Mal- 

 pighian tubules. These rest on the alimentary canal. They 

 are probably analogous to kidneys. 



(6) On either side of the alimentary canal find fan- 

 shaped groups of nearly colorless cords. Note that these 

 cords converge towards the spiracles. They are tracheae, 

 or air tubes. Remove one of the groups of tracheae with 

 its spiracle and examine with a microscope. Note the coils 

 of chitin. Draw. 



(7) Beneath these fan-shaped groups find longitudinal 

 cords, similar in structure to tracheae, next to the wall on 

 either side. These are the longitudinal tracheal trunks. 

 How many? 



(8) Make a diagram showing the above features (X2). 



