328 On the Young Stages of a few Annelids. 



bunch of thin bristles, two honk-shaped bristles instead of one. 

 The (esophagus is more clearly marked than in the preceding 

 stage ; the glands are found in all the rings except the last. In 

 the following stage, Fig. 28, there has been a still further 

 growth of the tentacles, and we find the pigment snots ar- 

 ranged both above and below in four parallel rows, the outer 

 rows being the smaller and less prominent. There are now four 

 hook-shaped bristles at the base of each of the dorsal cirri, 

 which are readily recognised as such in the rings immediately 

 following the seventh. The bunches of long bristles of the 

 four anterior rings are gradually losing their prominence, be- 

 coming less numerous in the present stage, and are replaced 

 by bristles similar to those of the ether bunch. At this period 

 the number of rings does not increase rapidly ; the principal 

 changes are confined to the growth of the dorsal cirri and of the 

 tentacles, as well as to changes in the pigment spots. When 

 examined in somewhat more advanced stages, Fig. 29, from 

 the lower side, we still have the pigment spots prominent and 

 well marked ; the only change consists in the lengthening of 

 the tentacles and the dorsal cirri, which are both fringed on 

 their anterior edge by vibratile cilia. 



On examining a young Polydora from the dorsal side, some- 

 what more advanced, Fig. 30, still having the same number of 

 segments in front of the anal ring, we find the four lines 

 of brilliant star-shaped pigment spots diminished to four 

 rows of dots ; the body has grown somewhat opaque and as- 

 sumed a reddish tinge, especially along the alimentary canal. 

 At about this period, also, the young begin to build their case, 

 secreting a copious viscid fluid (from the glands at the base of 

 the dorsal cirri?) to which particles of sand and mud become 

 attached as they creep along the bottom ; although they fre- 

 quently leave this case, they no longer possess the great power 

 of locomotion of the young larvae (Figs. 26-28) which moved 

 about rapidly by means of their rows of vibratile cilia and 

 bunches of long bristles. The pigment spots of the head have 



