2 1 4 Introduction to A jiiuml JMorfhology. 



tortuous in Lumbricus, &c., having an internal funnel- 

 or rosette-like opening into the body cavity, followed 

 by a straight or coiled glandular portion, and a small 

 narrow outer orifice, often in the next metamere to 

 that wherein is the funnel. The ciliated canal below 

 the intestine in Protula may also be an excretory 

 organ. 



The nervous system consists of a large double pre- 

 oral ganglion, each part often of 2-4 knots, sending 

 branches to the eyes and oral cirri. Its two compo- 

 nents may be close together (Enchytraeus), or sepa- 

 rated laterally (Aonis). Two lateral branches form a 

 ring around the pharynx, and unite below to form 

 two symmetrical chains of ventral ganglia, stretching 

 backwards, and giving off lateral branches. These 

 chains are remote from each other, and joined by 

 transverse commissures in tin- embryo and in adult 

 Serpul;e, &r. In other worms they approach in 

 the course of growth, and may coalesce into one cord 

 (anterior end of Terebella , in the centre of which runs 

 a thick distinct band of nerve tissue. The anterior 

 ganglia may be unequal (Clymene), and are usually 

 largest. Sometimes on each metameric branch at the 

 base of the parapodia little ganglia exist, also united 

 by longitudinal commissures (Pleione). 



A special nerve system, homologous to the azygos 

 nerve of the leech, and analogous to the sympathetic, 

 lies on the intestine, connected to the pre-oral ganglia 

 on the oesophagus, and when there is an epipharynx 

 sending branches to it, it expands backwards on the 

 intestinal wall, having special ganglia of its own, and 

 differs in texture from the ordinary systemic nerves. 



Sense organs are widely distributed. The cirri 



