On the Young Stages of a few Annelids. 335 



is as yet no trace of a division into oesophagus, stomach, and 

 intestine ; the main cavity still extends from the eye-specks 

 and trends towards the anal opening, gradually diminishing in 

 size. The chord of vihratile cilia have lost none of their 

 power, and it is quite remarkable how long these embryonic 

 features remain, even after the generic characters have become 

 well developed, and how early we can distinguish the family 

 to which our larva belongs. This is even more remarkable in 

 Polynoe, where before the young has more than six rings, it is 

 already a complete picture of the adult ; the same is the case 

 in young of Nereidse described by Milne Edwards* and Clapa- 

 rede,f the young worm, of not more than four rings, possessing 

 already all the generic features of the adult. 



These young larvae prosper readily in confinement; they 

 grow rapidly, passing in about ten days from the stage of Fig. 

 46 to that of Fig. 50. Subsequently the increase is somewhat 

 slower, and it requires about four weeks longer to find the 

 young Phyllodoce so far advanced that we can unmistakably 

 refer it to its proper species. In the next stage, Fig. 51, the 

 head and shield commence to lose the prominence they for- 

 merly' held, the two large tentacles lengthen considerably, and 

 two additional ones are formed on each side, thus making eight 

 long tentacles on the two sides of the now small rounded 

 shield ; the anterior tentacles become also somewhat more 

 prominent, as well as the lateral cirri from which project the 

 bristles, each bundle being composed of four or five, besides 

 the aciculum. In a somewhat more advanced stage, Fig. 52, 

 having twenty-five rings, Ave find the anal cirri slightly 

 lengthened, the broad lateral flappers are very distinct, the 

 small lateral cirri assuming nearly the shape they retain in the 

 adult. The head has also become shortened, the two pairs 

 of anterior antennae are equally developed, and the shield is 



* Edwards H. Milne; in Ann. Scieuc. Nat. 1845. III. p. 167. PI. 10, 

 Fig. 57. 



f Claparede A. R. E. Beobachtungen. ... PL XII. 



JUNE, 1866. 25 Akn. Ltc. Nat. Hist., Vol. VIII. 



