of a few Annelids » 217 



is different from that observed by Clapafede in T. conchilega, 

 where no such hook-shaped bristles were observed before the 

 fifth ring. The description given by Stimpson^ of the genus 

 Lumara agrees so well with some of the stages of Terebella, 

 that I am inclined to consider it only an embryonic condition 

 of some allied Terebella. Long after the stage here figured, 

 even when the branchiae have become quite well developed, it is 

 very common to fish up with the dip net these young Tere- 

 bell<B, which are capable of a certain amount of motion by the 

 contortions of the tentacles and body. They build their cases 

 very late, and frequently leave them, to climb about on eel-grass, 

 piles, &c., making considerable progress with the aid of their 

 tentacles, by which they drag themselves along. 



Pagenstecher has invariably represented the tentacles of the 

 anterior extremity of Spirorbis as developing symmetrically 

 and in pairs. This is not the case in our species, where they 

 are formed very differently from what has been thus far observed 

 in this family. We have between these two modes of growth 

 a difference similar to that existing between Terebella nebulosa 

 and T, conchilega, where in one case the tentacles appear suc- 

 cessively, while in the other they are formed in pairs. The 

 oldest tentacles of our Spirorbis are formed on the outside, new 

 tentacles appearing successively singly nearer the median line 

 on alternate sides, and not in pairs, the corresponding tentacles 

 on each side of the middle line being of very different lengths. 

 This want of symmetry is readily seen in the youngest speci- 

 mens figured (figs. 20, 21, 22) ; and though it is more diificult 

 to trace this in older stages (fig. 25), the presence of the simple 

 opercular tentacle always introduces a prominent asymme- 

 trical element, soon lost in the more advanced stages of the de- 

 velopment of Terebella. The two eyes are quite prominent, and 

 can generally be traced in the adult, although they are not so 

 striking as in the younger stages ; the ocular spots are always 

 limited to two, and we find at no time either a ring or clusters 

 of eye- specks. 



The first tentacle appears on the right (fig. 20 /,); next comes 

 the corresponding tentacle of the left, and only later (fig. 21) 

 the rudiment of the odd opercular tentacle (/q, fig. 22), cover- 

 ing in fig. 21 the right tentacle. The bristles make their ap- 

 pearance in fig. 21, where we find two of the three bundles 

 of the collar-like projection of the anterior extremity, always 

 distinctly marked in such young embryos. In the next stage 

 the collar is more prominent, and an additional bristle is found, 

 representing the third bundle of the collar (fig. 22). The pos- 

 * Marine Invertebrates of Grand Manan, 1853, p. 30. 



Ann. ^ Mag. N. Hist. Sen 3. Vol.xix. 15 



