THE WOOD-BORERS. 81 



In a number of cases, during tlie first summer, after several 

 spiders had been stored, we gently drew tbem out with a bent 

 wire. In one nest in wluch there were five spiders, we found, 

 two hours after they had been stored, that three were alive and 

 two were dead. In another, which the wasp had just begun to 

 seal up, were ten spiders. Three of these were injured in being 

 drawn out. Of the remainder four were alive and three dead. 

 On the anterior part of the dorsum of one of the living spiders 

 was the egg. It had probably been fertilized as the female car- 

 ried the male into the nest on her back. 



When we discovered ruhrocmctum in the straw-stack we 

 made many observations as to the position of the egg and the 

 number and condition of the spiders. We found that the egg 

 was always placed either on the side or the back of the anterior 

 part of the abdomen. The number of spiders stored was, as we 

 have already stated, from seven to fourteen. A fact that in- 

 terested us greatly was the remarkable accuracy shown by the 

 wasp in never selecting too large a spider for the calibre of the 

 straw. Oftentimes it was an extremely close fit, but it could 

 always be squeezed down. When they nested in posts they 

 used at times much larger prey. Unfortunately we never saw 

 this species capture its prey, nor could we prevail upon it to 

 sting in captivity, but the number of spiders that we found in 

 straws was so large as to afford abundant evidence concerning 

 the degree of surgical skill possessed by the wasps. Most of the 

 spiders taken by ruhrocinctum are inoffensive creatures and 

 there is no need to be careful or adroit in dealing with them. 



The concentration of the nervous system in the Aracknida 

 would seem to conduce very strongly to uniform results from 

 the stinging of the wasps. Unlike the larva used by Ammo- 

 phila, with its chain of ganglia, in the Araneidae the whole cen- 

 tral nervous system, including the brain and the ventral cord, 

 forms a single mass, pierced by the oesophagus. The greater 

 part of this mass^ which lies behind the oesophagus, represents 

 the fused ventral cord from which the nerves radiate. The 

 drawing (PI. VIII., fig. 8), gives a clear idea of this nervous 

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