164 MANUAL OF ZOOLOGY. 



system is well developed ; and there exists, in even greater 

 numbers, the same series of lateral sacculi which we have seen 

 in the Leeches, and which have either a respiratory or a renal 

 function. 



Of the little Na'ididce, the most familiar, is the Ttibifex rirn,~ 

 lorn/n't, which is of common occurrence in the mud of ponds and 

 streams. It is from half an inch to one inch and a half in 

 length, and of a bright red colour. The pseudo-haemal system 

 is provided with two contractile cavities or hearts ; and there 

 is present the same system of lateral tubes, opening externally 

 by pores, as occurs in the Earth-worms. 



The Na'ididce are chiefly noticeable on account of the singu- 

 lar process of non-sexual reproduction which they present, be- 

 fore they attain sexual maturity. In this process the Nai's 

 throws out a bud between two rings, at a point generally near 

 the middle of the body. Not only is this bud developed into 

 a fresh individual, but the two portions of the parent marked 

 out by the budding point likewise became developed into se- 

 parate individuals. The portion of the parent in front of the 

 bud develops a tail, whilst the portion behind the bud -de- 

 velops a head. Prior to the detachment of the bud, other 

 secondary buds are formed from the same segment, each in 

 front of the one already produced ; and in this way, before se- 

 paration takes place, a chain of organically connected indivi- 

 duals is produced, all of which are nourished by the anterior 

 portion of the primitive worm. 



ORDER III. TUBICOLA (Gephdhbranchiata). The Annelides 

 which are included in this order inhabit tubes, which may be 

 calcareous, and secreted by the animal itself, or may be com- 

 posed of grains of sand or pieces of broken shell, cemented to- 

 gether by a glutinous secretion from the body. The body- 

 rings are mostly provided with fasciculi of bristles set upon 

 lateral foot- tubercles or parapodia, by means of which the ani- 

 mal is enabled to draw itself in and out of its tube. The ali- 

 mentary canal is loosely attached to the integument. The 

 Tultieola are unisexual, and the young pass through a meta- 

 morphosis. 



When the tube of a Tubicolar Annelide is a true calcareous 

 secretion from the body of the animal, it is, nevertheless, 

 readily distinguished from the shell of the Mollusca, by the fact 

 that there is no organic connection of any kind between the 

 animal and its tube. 



The pseudo-haemal system has its usual arrangement, and 

 the contained fluid is usually red in colour, but is olive-green in 

 Sabella. The respiratory organs are in the form of filamentous 

 branchiae, attached to, or near, the head, generally in two late- 



