152 ANIMAL PHYSIOLOGY. [LESSON 43. 



A highly magnified view of the animal is given in Fig. 247, where 

 it will be seen that it possesses eight feet (c), like all the arachni- 

 dans. 



674. The mouth (b) is furnished with a proboscis, and is there- 

 fore suctorial ; it has also two short and thick maxillary palpi (a, a), 

 consisting of two joints, and above is a narrow upper lip. The ab- 

 domen is minutely ringed. 



675. No nutrimental organs have yet been discovered in these 

 parasites, partly because of their opacity, and partly on account of 

 the shining character of their integument. 



676. The next parasite originates the most loathsome, disgusting 

 disease that afflicts humanity the itch. Many medical men have 

 sought for this animal in vain, and hence they have concluded that 

 no such creature exists in connection with the disease. But their 

 failure has arisen from two causes : one, they have looked in the 

 wrong place, and the other, the animal is too minute to be seen by 

 unassisted vision, unless held up against the light. Usually they 

 are sought for in the pustule, characteristic of the' disease; but be- 

 fore the pustule can make its appearance, the Acarus has burrowed 

 off in another direction, and to succeed in finding it, the neighbor- 

 hood of the pustule should be explored with a needle. 



677. The Acarus scabicel (Fig. 248) possesses all the true char- 



acters of the Mites ; the legs in some mites, 

 terminate in suckers, but in this species (four 

 of them) in long setae (bristles a). 



678. The mouth has a twofold character, 

 it is adapted either for suction or mastica- 

 tion. The whole form of the animal adapts 

 it eminently for the life it leads, constantly 

 burrowing beneath the surface of the skin, 

 where, having no use for visual organs, none 

 appear to be present, as in the Mole. 



The Spiders are a very interesting class 

 of animals, the particulars in relation to them 

 requiring more space than the limits of this 

 Acarus scabitei wor ^ w afford ; suffice it to say, that the 



organs of digestion are arranged on a very 

 simple plan, as befits an animal strictly carnivorous. 



The mouth, as compared with the same structure in insects, is 

 also simple, and remarkably well adapted to the peculiar wants of 

 the animal. 



