240 LECTURE xr. 



those in Nephelis are not ciliated. In the earth-worm there are on 

 each side of the commencement of the intestine many looped tubes 

 which open externally by a small orifice on the under surface on one 

 side of the middle line, and have their inner surface beset with 

 festooned ciliated ridges. They are dilated near the orifice, and con- 

 tain a clear fluid, kept in movement by the action of the cilia; 

 which fluid the worms may obtain from the moist earth. These 

 " water-canals " are surrounded in Lumhricus by a remarkable plexus 

 of vessels, to which numerous pedunculated blood-receptacles are 

 appended, giving the whole system a racemose character. Similar 

 blood-sacs are appended to the same system of vessels in Nephelis 

 vulgaris ; but such sacs are simple reservoirs, and have no pulsation. 



The respiratory organs of the tubicolar anellids are in the form 

 of long, flattened, and sometimes tortuous, filaments* which radiate 

 from the head, generally in two lateral fasciculi, disposed in a funnel- 

 shaped or spiral form. "When not coloured by the red circulating 

 fluid, they are often barred and variegated by bright purple, green, 

 and yellow tints, forming a rich and gorgeous ornamental crown- 

 Each filament, in Serpula, Sabella, and Amphitrite, is fringed by a 

 row of actively vibrating cilia, which effect the requisite change of 

 the respiratory medium in contact with the vascular surface. In 

 Amphitrite they are semipinnate. In Terebella the branchial fila- 

 ments are florid blood-vessels, inclosed in a delicate non-ciliated 

 integument. The cephalic tentacles, which are hollow, and are pene- 

 trated by the chylaqueous fluid, expose an extensive surface to the 

 surrounding medium, which must react on the contained fluid, and 

 thus aid in respiration. 



The branchiae of the Annulata errantia are usually in the form of 

 shorter tufts than the cephalic ones of the Tubicola, and they are 

 attached to the upper parts of the sides of a greater number of seg- 

 ments. The following descriptions of some of their chief modifica- 

 tions are from the excellent "Report on the Anellida" above cited. 

 " Respiration is performed in Arenicola Piscatorum by means of 

 naked blood-vessels, projecting at the root of the setiferous process 

 upwards and outwards one-fourth of an inch in the adult worm from 

 the surface of the body. They are limited in number and distribu- 

 tion to the fourteen or sixteen middle annuli of the body. They are 

 commonly described as forming an arborescent tuft ; the division of 

 vessels is however regulated by a fixed principle. When fully in- 

 jected with blood, the vessels of each branchia form a single plane, 

 rising obliquely above and across the body, and immediately behind 



* Prep. No. 990. 



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