XIl] SPIDER 265 



pair of simple pouches opening into the endodermal intestine and 

 thus in their origin differing from those of Insects. The coxal 

 glands are better developed in some species, such as the common 

 House-spider, Tegenaria derhamii, than is the case in E. diademata, 

 where they are very degenerate and where their functions seem to 

 have largely passed to the Malpighian tubules. In fact these struc- 

 tures are an interesting example of a set of organs degenerating 

 and of their functions being assumed by another set. 



The heart of the Spider is of the same general type as that of 

 Myriapods ; it is a tube with paired slit-like openings ostia at 

 the sides, through which the blood enters to be driven out again 

 through certain rather ill-defined vessels to circulate in the spaces 

 between the various organs 





FIG. 119. Diagrammatic view of Palpal Organ. 



1. Tarsus. 2. Bulb. 3. Vesicula seminalis. 4. Opening of vesicul a 

 seminalis. 6. Conductor. 6. Haematodocha. 7. Alveolus. 



The nervous system is concentrated ; there is a bi-lobed ganglion 

 above the oesophagus which gives off nerves to the eyes and the 

 chelicerae ; this is connected by two lateral cords, which pass one on 

 each side of the oesophagus, with a large nervous mass situated in 

 the thorax. From this, nerves pass off to supply the remaining five 

 pairs of limbs and two nerves arise which pass backward and 

 supply the abdomen. The only conspicuous sense organs of Spiders 

 are the eyes, which are " simple " ; of these in E. diademata there 

 are four large eyes arranged in a square on the top of the head and 

 two small ones on each side of the square. This number, eight, is 

 not uncommon in Spiders, where both the number of eyes and their 

 disposition are much used in systematic classification. 



