ANNULATA. 



ANNULATA. 



is but slightly developed, the tissue beneath 

 the skin consisting of globular masses re- 

 sembling the general parenchyma of the 

 body ; and in this, peculiar cellular bodies 

 are often imbedded, resembling the urti- 

 cating organs of the polypes. These enclose 

 six, eight, or more 'rod-shaped bodies, 

 which are sometimes parallel with each 

 other, sometimes somewnat spirally curved. 

 The cell-membrane of these bodies subse- 

 quently disappears, and they frequently 

 project beyond the skin. Leydig figures 

 similar rod-shaped bodies as occurring in 

 the nuclei of the fat-cells situated beneath 

 the skin. 



In many of the Annulata, the muscular 

 fibres are grouped into distinct bundles, 

 serving to move the bristles, parts of the 

 mouth, &c. 



Beneath the skin at the ends of, or all 

 over the body, a number of peculiar glands 

 exist ; these consist at the closed end of a 

 nucleated cell (PI. 49. fig. 19 id), and a 

 long, somewhat coiled duct opening at the 

 surface of the body. 



The nervous system consists of a longi- 

 tudinal, single or double series of ventral 

 ganglia, connected by longitudinal cords; 

 the uppermost ganglion lies above the oeso- 

 phagus, and the two cords which connect it 

 with the second ganglion encircle this organ. 



The iippermost ganglion is enveloped in 

 a neurilemnia consisting of longitudinal 

 and transverse fibres, and not unfrequently 

 peculiar pigment-cells. The cords and 

 filaments are composed of extremely deli- 

 cate primitive fibres, between which, in 

 the ganglia, ganglion-globules are situated. 

 The filaments distributed to the body arise 

 principally from the ganglia. 



Many of the Annulata are furnished with 

 eyes ; these are usually denoted by the 

 brown, black, or red spots seen upon various 

 parts of the body. It is a disputed point 

 whether all these represent true eyes or 

 not ; but Quatrefages has described a lens, 

 transparent cornea and vitreous humour in 

 some of them, and he has no doubt that the 

 red points found at the sides of each ring in 

 several species of Nais are true eyes. 



In some Annulata, no distinct head is 

 present ; in others this is distinguishable by 

 its form, and is furnished with eyes and one 

 or more filaments, which are regarded as 

 antennae. In those in which the head is not 

 distinct, the mouth is situated at the anterior 

 end of the body ; in the others the mouth is 

 on the ventral surface, and is furnished with 



a muscular proboscis. The mouth is usually 

 surrounded by turgid lips, and sometimes 

 possesses a distinct dental armature (see 

 HIRUDO). The oral aperture is frequently 

 surrounded by a number of erectile tentacles 

 or cirri. 



The intestinal canal is usually straight, 

 and furnished with lateral appendages, or 

 constricted at intervals ; sometimes a sepa- 

 rate oesophagus, stomach and intestine are 

 distinguishable. The inner, and sometimes 

 the outer surface of the alimentary tube is 

 covered with ciliated epithelium. A yellow 

 or brown glandular layer surrounding: the 

 alimentary canal represents the liver. 



The general arrangement of the cir- 

 culatory system is, that two main vascular 

 trunks, one dorsal, the other ventral, tra- 

 verse the body longitudinally ; and the red 

 or green blood moves in the dorsal vessel 

 from behind forwards, whilst in the abdo- 

 minal vessel it moves from before back- 

 wards; these trunks being connected by 

 transverse vessels or meshes of them. The 

 anterior portion of the dorsal vessel is 

 usually broader, and appears to form the 

 rudiments of a heart. 



The respiration of the Annulata is effected 

 either by the skin ; by external gills in the 

 form of tentacular filaments or tufts, some- 

 times ciliated ; by ciliated depressions, or 

 by vesicles at the sides of the body. The 

 internal convolute ciliated canals, or water- 

 vessels, which were formerly considered 

 respiratory organs, are now regarded as 

 secretory tubes. In many instances a 

 transparent colourless liquid occupies the 

 interstices between the skin and the organs 

 of the body ; this contains colourless (rarely 

 coloured) corpuscles much resembling the 

 colourless corpuscles of the Vertebrata, and 

 is considered by some to represent the true 

 blood. 



The Annulata are propagated by trans- 

 verse division, by gemmation, and by means 

 of sexual organs. The embryos are at first 

 minute, rounded, and partially covered with 

 vibratile cilia. 



Order 1. CHJETOPODA (SETIGERA). Body 

 ringed, elongate, with feet or setigerous 

 rudiments of them ; external branchiae 

 usually present. 



Order 2. SUCTORIA (APODA). Body 

 elongate, ringed, without bristles or foot- 

 like tubercles ; locomotion by sucking-disks ; 

 no external branchiae. 



Order 3. TURBELLARIA. Body bilateral, 

 soft, covered with vibratile cilia, not seg- 



