342 On the Young Stages of a few Annelids. 



Fig. 24. Anterior extremity of a still older specimen, in which the 

 contrast between the opercular tentacle (t ) and the others (t l — 1 { ) 

 becomes very marked. 



Fig. 25. Young Spirorbis, in which all the characters of the adult can 

 be readily recognised. Lettering as above. 



Fig. 26. Young Polydoka having already lost the temporary bristles 

 of the anterior rings. 



Fig. 27. Somewhat older than the preceding figure, the pigment spots 

 of the anterior part are more marked (from below). 



Fig. 28. Older than figure 27, the dorsal cirri are quite apparent. 



Fig. 29. Young Polydora, seen from below, the pigment cells are 

 more concentrated than in the preceding stages. 



Fig. 30. Somewhat more advanced, seen from the dorsal side, the 

 pigment spots are reduced to mere dots, the number of rings has not 

 increased from the preceding stage. 



Fig. 31. Head of Polydora having forty rings. 



Fig. 32. Anterior of young Polydora, not quite full grown, from 

 below. 



Fig. 33. Adult Polydora seen from above. 



Fig. 34. Profile view of anal extremity of Polydora. 



Fig. 35. Profile view of the anterior extremity of Polydora. 



Fig. 36. Gland found at the side of each of the rings beyond the sixth 

 at the base of the dorsal cirrus. 



Fig. 37. Stiff bristles of the fifth ring. 



Fig. 38.* Small hook-shaped bristle of rings, following the fifth. 



Fig. 39. Young Neeine provided with the temporary bunch of bris- 

 tles. 



Fig. 40. Nerine in which the tentacles and dorsal cirri have begun to 

 develop, which has lost the large bunch of serrated bristles. 



Fig. 41. Somewhat more advanced than figure 40. 



Fig. 42. Young Nerine, having most of the characters of the adult. 



Fig. 42a. Portion of one of the serrated bristles of the temporary clus- 

 ter of figure 39. 



Fig. 43. Anterior extremity of an adult Nerine, seen in profile. 



* This figure was accidentally numbered 33 on Plate IX., it is fig. 33 be- 

 tween fig. 36 and fig. 84. 



