of a few Annelids. 253 



Quatrefages, and Miiller) Krolin, Max Miiller, Van Beneden, 

 AVagener, Schneider, Keferstein, Pa2:en steelier, and others, but 

 more especially Claparede, have lately done so much to advance 

 our knowledge of the development of Annelids, we can hardly 

 be said to have more than commenced the investigation of the 

 development of the Annelids proper, which in this respect are 

 far behind the intestinal worms; and we must wait for further 

 observations before classifications of embryonic Annelids can be 

 of material advantage for systematic studies. 



Among the young Annelids not yet traced to their adult 

 condition, I would figure two forms totally unlike any hitherto 

 described. They both come in the group of Metacha^tse of 

 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 slightest 

 trace of bristles along the sides of the distinctly articulate body. 

 We find on the anterior extremity, on each side, immediately 

 behind the tentacles an immense cluster of long, smooth setse, 

 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 (^ inch in length) 

 I have frequently fished up, throughout the summer, with the 

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

 })erhaps 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 w^e 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 retro- 

 grade development so much more remarkable than the one de- 

 scribed above in the Nareda-like worm, that it seems scarcely 

 ])Ossible. The number of rings is also different, yet the general 

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

 larvre, 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 



