3 68 



PHYLUM ARTHROPODA. 



bends down on the basal joint in " sub-chelate " fashion, and is per- 

 forated by the duct of a poison gland. 



2. The leg-like, usually six-jointed, non-chelate pedipalpSj whose 

 basal joint helps in mastication, while the terminal joint in the male 

 expands as a reservoir for the spermatozoa and serves as a copulatory 

 organ. 



3-6. Four pairs of terminally clawed 7 -jointed walking legs. The 

 most anterior pair are much used as feelers. The spinnerets at the 

 end of the abdomen are modified abdominal legs. Besides these the 

 embryo has four pairs of abdominal appendages which abort. 



FIG. 192. Garden spider. 



I., Female garden spider; II., end view of head of the same 

 showing the simple eyes, the poison fangs (ch.), and the 

 pedipalps (/*.)> III., posterior end of body showing two pairs 

 of spinnerets (j/.)> with anus above. 



The nervous system is of the usual Arthropod type, but 

 shows much centralisation. Thus the ventral ganglia are 

 fused into one large centre in the cephalothorax (see Fig. 

 193), a condition comparable to that in crabs. There 

 are two or three rows of simple eyes on the cephalothorax, 

 whose focal distance is very short, spiders trusting most 

 to their exquisite sense of touch, by which thev discriminate 



