of a few Annelids. 251 



to deal with a Phyllodoce. A second pair of small anterior 

 tentacles is budding at the base of the first. Though the 

 digestive cavity opens externally at the mouth and anus, there 

 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 vibratile 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 be- 

 fore 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 Claparedef, the young worm 

 of not more than four rings possessing already all the generic 

 features of the adult. 



These young larvse thrive 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 unraistakeably 

 refer it to its proper species. In the next stage (fig. 51) 

 the head and shield begin to lose the prominence they for- 

 merly held, the two large tentacles lengthen considerably, and 

 ±wo 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 pro- 

 minent, 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, we 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 antenna; 

 are equally developed, and the shield is reduced to a small 

 circular patch. The changes henceforth are limited to the head, 

 to the increase of the broad flappers and anal cirri, and to the 

 diff'erent degrees of development of the antennrc, placed, in the 

 stage of fig. 52, directly one behind the other, although at the 

 outset they originate one beneath the other; there is no trace 

 to be seen of the rings corresponding to these antennse, as wc 

 should expect theoretically. They lose little by little the ring 

 of vibratile cilia; the head elongates; the eyes are brought 

 nearer the base of the antennse, until finally the anterior part of 



* Ann. Scien. Nat. 1845, iii. p. 167, pi 10. fig. 6/. 

 t Beobachtungen, pi. 12. 



