33S On the Young Stages of a few Annelids. 



Claparede ; and though I cannot refer them to their minor sub- 

 divisions, they already show most remarkable features. One 

 of them (Fig. 56) reminds us somewhat of Polydora on account of 

 the shape of its head and tentacles ; it has, however, already a 

 distinct oesophagus, stomach, and intestine, and not the slight- 

 est trace of bristles along the sides of the distinctly articulate 

 body. We find on the anterior extremity on each side imme- 

 diately behind the tentacles, an immense cluster of long smooth 

 setae, seven to eight in each pencil, nearly twice as long as the 

 young worm. The posterior ring is edged with vibratile cilia, 

 and terminates in a club-shaped appendage ; the eyes are dis- 

 tinct, two in number. This little worm (-^-of an inch in length) 

 I have frequently fished np throughout the summer with the 

 dip-net, but unfortunately always in the same stage. "We have 

 perhaps here again a case similar to that of Loven's larva, de- 

 scribed above, of a young worm, having articulations and well 

 developed appendages, which has reached a condition when in 

 other Annelids the temporary bristles have vanished, the per- 

 manent ones replacing them, and in which we find as yet no- 

 thing to tell us to what genus our larva may belong. Were I to 

 be guided by analogy (especially on account of the perfect 

 differentiation of the stomach, oesophagus, and intestine, 

 which are always divided late in the larval condition in other 

 Annelids, long after the generic characters have appeared), 

 I should be strongly tempted to consider it the embryo of the 

 young worm represented in Figure 57. This would involve a 

 case of retrograde development so much more remarkable than 

 the one described above in the Nareda-like worm, that it seems 

 scarcely possible. The number of rings is also different, yet 

 the general aspect of the head, and particularly the lightning- 

 speed of the larvae, darting off like a shot from perfect rest, 

 are points of great similarity, and I give this suggestion for 

 what it may be worth. The changes to be undergone are of 

 the same nature as in Nareda, the tentacles must disappear, 

 the temporary bristles drop off', and the articulations become 



