SECT. v. ERRASTIA. \ 57 



holds it firmly while the re-inversion of the sac draws it 

 into the body to be digested. This apparatus is un- 

 armed in the genera Arenicola, Phyllodoce, and others, 

 but in the Nereis it has one pair of strong curved horny 

 jaws. In the Eunice there are three toothed jaws on 

 one side and four jaws on the other side of the gullet, 

 each pair having a different form, and the tiny Lombri- 

 nereis has eight little black hooks which are seen 

 through its pellucid tissues, snapping like so many pairs 

 of hooked scissors. The Errant Worms are voraciously 

 carnivorous, and when the gullet is turned inside out 

 the toothed jaws project, seize the prey, and drag it into 

 a ciliated alimentary canal, for there is no proper 

 stomach in these worms. The canal is generally straight, 

 and terminates in a vent at the posterior end of the 

 body. 



The respiratory organs of the Errantia are external 

 gills of great variety of forms : they are chiefly like 

 branching trees, or filamentary bushes, traversed by ca- 

 pillary bloodvessels. They are sometimes small, and 

 arranged on every segment along both sides of the back ; 

 sometimes they are large and fixed only at intervals. 

 Like the lower Annelids, they have two liquid systems, 

 one red and the other colourless, and the circulation of 

 the blood is the same ; but as the pulsations of the vessel 

 behind the head are too feeble to send the blood through 

 the labyrinth of capillary vessels in these long worms, 

 there is a supplementary heart, or pulsating vessel, in 

 each segment of the worm, which partakes in and 

 facilitates the general circulation. 



The Eunice and other very long worms may have 

 hundreds of these centres of propulsion, which make 

 the circulation rapid ; and it is increased by the rest- 

 lessness and activity of the worms themselves, which 

 bring their gills perpetually into new strata of water. 



The nervous system of the Errantia consists of a 



