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50 Poisonous Arthropods 



that if the nettling hairs are mingled with blood, they immediately 

 produce a change in the red corpuscles. These at once become 



coarsely crenated, and the 

 roleaux are broken up in the 

 vicinity of the hair (fig. 37b). 

 The corpuscles decrease in 

 size, the coarse crenations 

 are transformed into slender 

 spines which rapidly disap- 

 pear, leaving the corpuscles 

 in the form of spheres, the 

 hght refraction of which con- 

 trasts them sharply with the 

 normal corpuscles. The 

 reaction always begins at the 



(o) Ordinary hairs and three poison hairs of sub- , 1 -u ^ •*,4- ^J^ a-U^ U^:^ 



dorsal and lateral tubercles of the larva of the DaSai Snarp pOlUt 01 tnc nair. 

 browntaU moth. Drawing by Miss Kephart. j^ ^^^^ ^^^ ^^ produCcd by 



purely mechanical means, such as the mingling of minute par- 

 ticles of glass wool, the barbed hairs of a tussock moth, or the other 

 coarser hairs of the brown-tail, with the blood. 



The question of the source of the poison has been studied in our 

 laboratory by Miss Cornelia 



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37, 



Kephart. She first confirmed 

 Dr. Tyzzer's general results 

 and then studied carefully fixed 

 specimens of the larvae to 

 determine the distribution of 

 the hairs and their relation to 

 the underlying tissues. 



The poison hairs (fig. 37), 

 are found on the subdorsal 

 and lateral tubercles (fig. 38), 

 in bunches of from three to 

 twelve on the minute papillae 

 with which the tubercles are 

 thickly covered. The under- 

 lying hypodermis is very 

 greatly thickened, the cells 

 being three or four times the length of the ordinary hypodermal 

 cells and being closely crowded together. Instead of a pore canal 



(&) Effect of the poison on the blood cor- 

 puscles of man. After Tyzzer. 



