326 On the Young Stages of a feio Annelids. 



sessed them, the bunches of ringed bristles so characteristic of 

 the younger stages of many Annelids, such as Leucodora Clap., 

 Nerine, and Spio. The tentacles of the head are de- 

 veloping, and there remain but slight traces round the head 

 and anus of the former rings of vibratile cilia, as well as very 

 narrow bands of short vibratile cilia on the dorsal side ; similar 

 bands are found on the lower side composed of larger cilia, 

 which greatly assist in locomotion. These bands are less pow- 

 erful towards the extremities, being greatly developed towards 

 the middle, especially on the lower side. The vibratile ring 

 surrounding the anus is less prominent than in Claparede's em- 

 bryo ; the anterior and posterior rings of cilia, as well as the 

 transverse bands, diminish rapidly in size with advancing age, 

 so much so that in Fig. 28 they have almost totally disap- 

 peared. In the youngest stage seen, Fig. 26, there are four 

 well developed anterior rings, each provided with an upper 

 and lower bunch of bristles, the dorsal bunch being the longest, 

 and diminishing in length as it recedes from the head, the 

 lower bunches consisting of bristles of the same length ; the 

 fifth ring (r 5 ) is much wider than any other, and has only 

 three short, stout bristles on each side ; then comes the sixth 

 ring, each having a bundle of bristles similar to those of the 

 smaller cluster of the four anterior rings ; in the subsequent 

 rings, which are nearly equally developed, having a slight 

 lateral swelling and rudimentary dorsal cirrus, we find a similar 

 bundle of bristles, and in addition, in the seventh, eighth, and 

 ninth, a single hook-shaped bristle : while immediately in 

 front of the anal extremity the rudimentary rings have merely 

 a couple of thin bristles. The three rings following the sixth 

 have rudimentary glands (g) first observed in this genus by 

 Claparede in his description of Polydora ; they consist, how- 

 ever, of a smaller number of glands, only two or three in each 

 bag. The general color of Polydora at this period is quite a 

 delicate grey, of a yellowish tinge, with a bright yellow line 

 along the middle of the back, and following the outline of the 



