4-50 THE MICROSCOPE. 



The Serpula, if withdrawn from its calcareous tube (fig. 

 219), is found to have the lower part of the body composed 

 of a series of flattened rings, and entirely destitute of limbs 

 or other appendages. Its food is brought to its mouth 

 by currents created by the cilia on the branchial tufts. 



Of Errantia, the family Aphrodttce, better known as 

 Sea-mice, are the more remarkable. In these animals the 

 form of the body is long and ovate ; the head small, and 

 furnished with very short tentacles; the feet large, with 

 immense tufts of bristles and spines, often of the most re- 

 markable forms, and exhibiting exceedingly brilliant metal- 

 lic colours. Each tuft of hair is retractile within a horny 

 sheath, which not only serves to protect the soft parts of the 

 animal from injury, but as weapons of defence. Another 

 peculiarity is, that the dorsal surface is entirely or partially 

 covered by a double series of large membranous scales 

 attached to the alternate segments, between which the 

 beautiful bristles of the feet make their appearance. These 

 animals generally inhabit deep water, although numbers of 

 them are thrown upon our coasts after a storm. 



ACARINA PARASITES. Nearly all the animals in- 

 cluded in this order, of which the common Mites are the 

 best known examples, are recognisable at the first glance 

 by the form, of the body, which usually constitutes a 

 roundish or oval mass, without a trace of segmentation. 

 They are mostly parasitic animals, furnished with a pro- 

 boscis having a pair of sharp spines, which serve for cut- 

 ting and wounding, and on each side of the same a palpus. 

 The proboscis is jointed and retractile; and sometimes it 

 has an enlarged base, which has been called a head. The 

 eyes, which are frequently wanting in parasites, are two in 

 number when present, and placed on each side of the 

 anterior portion of the body. Acarina are generally ovi- 

 parous; a few bear living young, and these possess only 

 three pairs of feet; the fourth pair do not make their 

 appearance until after the first moult. 



Parasites infest the skin, lurk among the hairs of quad- 

 rupeds, the feathers of birds, and even of many insects, 

 whence they draw an abundant supply of nourish- 

 ment for their singular mode of existence. Mr. Henry 

 Denny figured and described a greater number of parasitic 



