PHYLUM ARTHROPOD A 



307 



mouth. The fleshy frg.s number from seventeen pairs to over 

 forty pairs in different species; each (Fig. 229, F.I) bears two 

 claws. The anus is at the posterior end; the genital pore is 

 situated between 

 the last pair of 

 legs; and a ne- 

 phridiopore lies 

 at the base of 

 each leg. The 

 skin is covered 

 with papilla, 

 each bearing a 

 spine; these pa- 

 pillce are especi- 

 ally numerous on 

 the antennte, lips, 

 and oral papillae, 

 and are probably 

 tactile (Fig. 229). 

 The digestive 

 system (Fig. 230, 

 8) is very simple, 

 consisting of a 

 muscular phar- 

 ynx, a short 

 oesophagus, a long, 

 saccular stomach, 

 and a short intes- 

 tine. The pair 

 of salivary glands 

 (n), which open 

 into the mouth cavity, are modified nephridia. The heart is 

 the only blood-vessel; it is a dorsal tube with paired ostia 

 connecting it with the pericardial cavity in which it lies. The 

 body-cavity is a blood space, i.e. a hgemoccel. The breathing 



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