EliRANTIA.- 



-ANNELIDA.- 



-EliRANTIA. 



295 



The calcareous tubes in which others dwcl), are secreted 

 liy a collar surrouudiug the first segment of the body. 

 —{Slebold.) 



liciiroductiou takes place partly by a transverse 

 iissnratioii, and partly by a sexual apparatus. Those 

 species which undergo the process of division never 

 possess genital organs at the time it is taking place ; 

 but after this process ceases genital organs are deve- 

 loped, and reproduction takes place by eggs. " The 

 extreme vulnerability and reproductive power of many 

 Cho3topodes give rise to their frequent multiplication by 

 artiticial and accidental division. The fragments thus 

 produced are finally developed, and the mutilated animal 

 ultimately regains its lost parts. Some have the power 

 of voluntary division from the least handling of their 

 body, and these separated parts are probably developed 

 to new individuals." — {Siehold.) 



Most of the species have separate sexes, but in the 

 Leeches and Earth-worms the two are always united 

 in the same individual. In by far the greater number 

 of the Annelides (those which have the body provided 

 with bristles as organs of locomotion), the young undergo 

 a complete metamorphosis. The euibryo, immediately 

 it escapes from the egg, swims freely about like an 

 infusorial animalcule, by means of the ciliated mem- 

 brane which covers its whole body. This disappears, 

 the embryo lengthens, eyes appear upon the anterior 

 extremity, the body becomes divided into segments, 

 and bristles, &c., make their appearance. 



The Auuelides vary considerably in their manner of 

 life, and this, along with the structure of their breath- 

 ing apparatus, has induced MM. Audouin and Milne 

 Edwards to divide them into four orders : — 



I. Errantia, those in which the respiratory organs 

 are attached to the dorsal surface of the body along the 

 whole or greater part of its length, hence called Dorsi- 

 hranchiata by Cuvier and others. These species are 

 found living a free and wandering life, crawling actively 

 in mud or swimming in the water. 



II. 'Tuhkola or Scdentaria, those in which the 

 respiratory organs are formed like plumes, attached to 

 the head or anterior portion of the body, hence called 

 by many authors Capitohranchiuta. These species 

 live a sedentary life, and are found, with few exceptions, 

 having their abode in tubes. 



III. Terricola or Earth-worms, those in which the 

 resi>iratory organs are internal, being in the form of 

 small vesicles oiiening externally by very minute pores. 

 These are found making their dwelling-place in soft 

 earth, piercing the ground in all directions. 



IV. Suctoria or Suckers, those in which the respira- 

 tory organs are internal, like the preceding order, and 

 disposed in the form of small membranous sacs, each 

 of which communicates externally by a minute orifioe 

 on the ventral aspect of the body. They possess no 

 bristles, but are provided with suctorial discs by which 

 they progress. These are all natives of the water, and 

 uuiny are found living partially as parasites upon fishes. 



OuDEU I.— ERRANTIA {■=Dorsih-anchiata). 



All the species belonging to this order are aquatic, 

 crawling with activity in the mud or swimming with 



facility in the water. The body in some of them is 

 very long and slender — some species in the equatorial 

 seas attaining the length of five feet — in others broad 

 and rather short. Their head is distinct from the 

 trunk, and is furrjished with two pairs of rudimentary 

 eyes, a certain number of conical or filiform appendages 

 which are distinguished into antennre, palpi, and ten- 

 tacles, and a mouth furnished with a proboscis which 

 can be protruded at will, and often armed with strong 

 horny jaws. The body is composed of numerous 

 narrow segments or rings, varying in number from 

 twenty to five hundred. In the majority of the species 

 each segment or ring has on each side an organ which 

 many naturalists call a foot. It is in the form of a 

 fleshy tubercle ; is composed of two divisions placed one 

 above the other called rami, or branches ; and provided 

 with one or two brushes of bristles. These bristles are 

 of two kinds, subulate and hooked, and the animal can 

 protrude them considerably by means of muscles appro- 

 priated to that use. In addition to these bundles of 

 bristles, tlfere are attached to these feet a number ot 

 soft and blunt appendages, called cirrhi. They are 

 usually two to each foot, but their number and position 

 vary considerably. They are either in the form of long, 

 subulate, fleshy tentacles, or merely compressed leaflets 

 or papillary tubercles. In general they are partially 

 contractile. The gills or branchise vary much in form, 

 number, and position. In some the organ assumes the 

 form of arbuscles or tufts, or fan-shaped crests ; in a 

 second series it is a simple or pectinated filament; and 

 in a third it is a nipple-like lobe, or merely a mem- 

 branous tubercle. In general they are placed along 

 the back, but sometimes they are arranged along the 

 sides or at the taU. 



" Organized for locomotion," says Dr. Johnston, 

 " this tribe of Annelides — the tyrants or the aristocracy 

 of their race — wander abroad, and are in constant war- 

 fare with all around them. They crawd on the surface 

 at a pace that varies in the species from extreme slow- 

 ness to energetic activity. Many of them swim with 

 ease, and others burrow in the wet sand of the shore. 

 They are eminently carnivorous, with the exception 

 perhaps of the AriciidcB, which may bo geodeiihagous 

 or feeders on putrescent matter." Some of them appear 

 to be truly pelagian, and are only met with in the high 

 seas ; but the great majority dwell between tide-marks 

 on the shore, where they find refuge and concealment 

 under stones, or among corallines and sea-weeds. A 

 small number burrow in the sand, in which they form 

 a sort of sheath by a glairy secretion from the skin, 

 and a few are truly tubiculous ; but these sheaths are 

 not indispensable, and can be occasionally abandoned 

 without inconvenience. The mouth, as has been 

 stated, is well adapted for their rapacious manner of 

 life ; but in addition to these organs of olTenee, these 

 animals are likewise provided with organs of defence 

 against their enemies. The principal ones are the 

 bristles with which the segments of their body are pro- 

 vided. " Some Annelidans when alarmed, such astho 

 Aphrodites, instinctively contract the body into a sort 

 of ball, bringing the head and tail into near contact, 

 and in this manner seem anxious to elude the danger. 

 Others, that have a long vermiform body, wriggle and 



