ANNULOSA: ANNELIDA. 183 



bristles, attached in rows to the sides and ventral surface of 

 the body. They are all hermaphrodite. 



In the common Earth-worm (Lumbricus) the body is cylin- 

 drical, attenuated at both extremities, and carrying in the 

 adult a thickened zone, which occupies from six to nine rings 

 in the anterior part of the body, is connected with reproduc- 

 tion, and is termed the " clitellum," or "saddle." Locomo- 

 tion is effected by eight rows of short bristles or setae, four of 

 which are placed laterally and four on the ventral surface of 

 the body; these representing the foot-tubercles of the higher 

 Annelides. The mouth is edentulous, and opens into a short 

 oesophagus, which leads to a muscular crop, or "pro-ventri- 

 culus," succeeded by a second muscular dilatation, or gizzard. 

 The intestine is continued straight to the anus, and is con- 

 stricted in its course by numerous transverse septa, springing 

 from the walls of the perivisceral cavity. The pseudo-haemal 

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

 numbers, the same series of lateral sacculi or "segmental 

 organs " which we have seen in the Leeches, and which have 

 either a respiratory or a renal function. In all the Oligochata 

 the segmental organs communicate internally with the perivis- 

 ceral cavity as well as externally with the outer medium. A 

 portion of the segmental organs is ciliated, and in all cases 

 the segmental organs of certain of the segments have the 

 special function of acting as efferent ducts for the generative 

 organs. 



Of the little Ndididcz, the most familiar is the Tubifex rivu- 

 lorum, 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 Naididcz 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 Ndis 

 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 1 portion of the parent in front of the 

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

 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 separation takes 



