ANNULOSA, OR WORMS. 



19T 



FIG. 407. 



\ 



corpusculated fluid which moves in the peri-visceral cavity of the body 

 and in its extensions, is that which really represents the blood of other 

 Articulated animals; and that the system of vessels carrying the red fluid 

 is to be likened on the one hand to the ' water- vascular system ' of the 

 inferior Worms, and on the other to the tracheal apparatus of Insects 

 ( 634). In the observation of the beauti- 

 ful spectacle presented by the respiratory 

 circulation of the various kinds of Anne- 

 lids which swarm on most of our shores, 

 and in the examination of what is going 

 on in the interior of their bodies (where 

 this is rendered, possible by their trans- 

 parence), the Microscopist will find a most 

 fertile source of interesting occupation; 

 and he may easily, with care and patience, 

 make many valuable additions to our pre- 

 sent stock of knowledge on these points. 

 There are many of these marine Annelids, 

 in which the appendages of various kinds 

 put forth from the sides of their bodies fur- 

 nish very beautiful microscopic objects; as 

 do also the different forms of teeth, jaws, 

 etc., with which the mouth is commonly 

 armed in the free or non-tubicolar species, 

 these being eminently carnivorous. 



595. The early history of the Develop- 

 ment of Annelids, too, is extremely curi- 

 ous; for they come forth from the egg in a 

 condition very little more advanced than 

 the ciliated gemmules of Polypes, consist- 

 ing of a globular mass of untransformed 

 cells, certain parts of whose surface are 

 covered with cilia; in a few hours, how- 

 ever, this embryonic mass elongates, and 

 the indications of a segmental division be- 

 come apparent, the head being (as it were) 

 marked off in front, whilst behind this is 

 a large segment thickly covered with cilia, 

 then a narrower and non-ciliated segment, 

 and lastly the caudal or tail-segment, which 

 is furnished with cilia. A little later, a 

 new segment is seen to be interposed in 

 front of the caudal; and the dark internal 



Circulating Apparatus of Terebella 

 conchilega:a, labial ring; 6, 6, ten- 

 tacles ; c, first segment or the trunk ; 

 d, skin of the back; e, pharynx; /. 

 intestine; g, longitudinal muscles of 

 the inferior surface of the body; h, 

 glandular organ (liver ?) ; i, organs of 

 generation; j, feet; fc, fc, branchiae; 

 I, dorsal vessel acting as a respira- 

 tory heart; m, dorso-intestinal vessel ; 

 n, venous sinus surrounding oesopha- 

 gus; /, inferior intestinal vessel; o, 

 o, ventral trunk; p, lateral vascular 

 branches. 



granular mass shapes itself into the out- 

 line of an alimentary canal. 1 The number 

 of segments progressively increases by the 

 interposition of new ones between the caudal 

 and its preceding segments; the various-internal organs become more and 

 more distinct, eye-spots make their appearance, little bristly appendages are 



1 A most curious transformation once occurred within the Author's experience 

 in the larva of an Annelid, which was furnished with a broad collar or disk 

 fringed with very long cilia, and showed merely an appearance of segmentation 

 in its hinder part; for in the course of a few minutes, during which it was not 

 under observation, this larva assumed the ordinary form of a marine Worm three 



