3o6 



ARACHNOIDEA. 



^^ A full description, with careful figures, will be found in the Bulletin 

 of the Society of Moscow, i860. It is a very flat, broad species; 

 and the absence of spines on the back at once distinguishes it 



Sarcoptes mutans, side view. Copied from Robin. 



from all the preceding. The ailment produced by it, is observed 

 most frequently on the hen and the cock, appearing first on the 

 feet, on the comb, and about the beak. No premonitory symptoms 

 indicate its approach. The fowls preserve their appetite and live- 

 liness ; although sometimes a careful observer may see that the 

 sick animals shake their heads, raise and stretch their legs in 

 a convulsive manner. If the examination is followed up, some 

 white points and lines traced in zigzag, covered by very small 

 scales, which the least rubbing knocks off, may be seen on 

 the comb. The skin, covered by them, is lightly chagrined 

 and of a brown colour, which contrasts with the red colour 

 of the rest of the comb. At that period no lesion of the 

 tissues is observable. The malady remains stationary for fifteen 

 days or even a month, at the end of which time the base 

 of the comb thickens and becomes darker, and the linear tracings 

 assume the appearance of true burrows of the itch insect, and at 

 the bottom of them the Sarcoptes mutans is to be found. At 

 a later period the feathers of the head and about the beak 

 undergo a remarkable change : they turn back, stand on end, 



