A CENTIPED 23 
of maxille, the second pair of which is homologous to the 
labium of insects. 
Exercise 3. Remove, under a dissecting microscope, the prehen- 
sile hooks and the mouth-parts, beginning with the pos- 
terior ones and working forward, and the antenne. Mount 
them on a slide and draw an outline of each. Compare 
the different structures of the mouth-parts with those 
of the insect and label them all. 
The internal organs. The digestive, circulatory, respiratory, 
excretory, and nervous systems are essentially like the same 
systems in insects. The reproductive system consists of a 
pair of sexual glands with paired ducts, the posterior portions 
of which unite to forma common duct. This opens to the 
outside in the genital segment, which is the penultimate body 
segment. 
