sSIO Mr. A. Agassiz on the Young Stages 



to the most advanced stage he observed is somewhat abrupt. I 

 have been able to supply this defect in the observations given 

 below (see figs. 7-16). Although uiy larvse differ somewhat 

 from those of Loven, there can be no question of the family 

 identity of the two. In the youngest larva (fig. 3) we find, as 

 observed by Loveu, no trace as yet of any articulations; but we 

 have, besides the large circle of vibratile cilia round the anterior 

 extremity {v) described by Loven, a similar powerful ring {v') 

 round the posterior extremity. This anal circle either does not 

 exist in Loven^s larva, or must have escaped his attention. Our 

 larva is, hte Loven^s, transparent as glass; it has in addition, 

 following the course of the two vibratile rings, a single row of 

 most brilliantly coloured orange pigment spots of different shades 

 and sizes ; similar pigment spots are scattered in three unequal 

 rows along the unarticulate body between the anal and anterior 

 vibratile chords ; there is besides a crescent-shaped row of spots 

 along the posterior edge of the mouth (m). The two jet-black 

 eye-spots \e) on each side of the summit of the disk are also 

 found in our larva (seen only when facing the ventral or dorsal 

 side, as in fig. 7). The eyes have a totally different appearance 

 from the other pigment spots found along the body and vibra- 

 tile rings. They are apparently connected with a nervous gan- 

 glion sending off delicate branches to the anterior vibratile ring. 

 The mouth opens behind the anterior vibratile chord, leading 

 into a well-defined oesophagus communicating with a stomach, 

 which is distinctly separated at its posterior extremity from the 

 intestine ; the latter opens externally in the middle of the anal 

 vibratile chord, placed at the base of the anal ring; this is 

 slightly conical, and projects somewhat beyond the vibratile 

 chord. 



Loven distinctly states that the rings are formed immediately 

 at the base of the anterior disk behind the mouth : this is pro- 

 bably an error of observation, owing to the advanced period at 

 which the articulations first commence ; or the rings are simply 

 folds due to contraction. He describes all the rings of his young 

 larva (Loven, fig. 2) as made up of four pieces, and represents 

 the same thing a-gain in his fig. 5. Nothing of the kind could 

 be seen in the formation of the rings in our larva (figs. 4 & 5) . 

 In somewhat more advanced stages, after the first rings were 

 distinctly developed, I had no difficulty in finding near the anal 

 ring a small part of the body of the worm in which the articu- 

 lations became more and more distinct as they were more distant 

 from the anus (fig. 6), showing beyond doubt that new rings 

 are formed between the anal rings and the older anterior rings, 

 as in other Annelid larva?, and not immediately below the disk 

 near the mouth as stated by Loven. The larvse figured by 



