452 



ANNELIDA. 



grooves in Polygordius, and by ciliated rings in Protodrilus. There 

 is a median ciliated groove extending along the ventral surface of 

 Protodrilus. The segmentation is homonomous and is marked by 

 the coelomic septa (Fig. 361, d). There are no circular muscles in 

 the body-wall. 



The cerebral ganglion is in the preoral lobe, and the ventral 

 cords lie in the epidermis (Fig. 359), and are without ganglionic 

 swellings ; in Protodrilus they are separated, one being placed on each 



FIG. 359. Polygordius neapolitamts. b, dorsal view of head and anterior part of body, 

 showing the ciliated pits, c, hind end showing the last three segments, and the anal 

 segment with a circle of papillae, and the anus (after Fraipont). 



side of the ventral groove; while in Polygwdius* they are fused. 

 There is in Polygordius a very short eversible buccal region followed 

 by an oesophagus, which does not extend beyond the head (peri- 

 stomial part). In Protodrilus there is a U-shaped muscular tube 

 placed ventral to, and opening into the oesophagus. 



There is a dorsal and ventral mesentery, and oblique longitudinal 

 septa passing across the body-cavity on each side from the region 



>, 



* In Polygordius there is a fine canal in the ventral cord, which is said to be 

 a remnant of the ventral ciliated groove of the larva. 



