On the Young Stages of a few Annelids. 329 



disappeared except four prominent eye-specks, the same 

 number as found in the adult, in which, however, they are far 

 less conspicuous than in this stage of the young. 



When the young worm lias already thirty-five rings, there 

 have been no changes of any consequence besides the further 

 lengthening of the dorsal cirri and the increase of the nidi- 

 mentary cirrus at their base, which can first be traced in Fig. 

 29 ; two small tentacles have been formed at the anterior part 

 of the head, Fig. 31. The number of bristles of the fifth ring 

 has increased to five, and the number of glands in each enve- 

 lope to eight or ten. In nearly full-grown specimens, when 

 seen from below, these glands are particularly prominent, Fig. 

 32, as well as the six hook-shaped bristles at the base of the 

 short cirrus. The black pigment clots have all disappeared, 

 and the worm is gradually assuming a darker tinge, the fifth 

 ring has increased in width, the larger of its bristles assuming 

 the shape they have in the adult, as in Fig. 37, with a slight 

 notch at their swollen exterior extremity. The simple hook- 

 shaped bristles of the seventh and succeeding rings, have de- 

 veloped a slight process on the convex side, with a stiff bristle, 

 Fig. 38, extending from the base of the curve, as in the adult 

 Polydora. The anal ring has taken a somewhat funnel shaped 

 form, w r ith which the little worms can attach themselves quite 

 firmly ; the adult makes use of this anal disk, Fig. 34, almost 

 as freely as the sucking disk of a leech. 



In the adult, Fig. 33, the dorsal cirri equal in length the 

 thickness of the body, and have lost their vibratile fringe; the 

 glands have taken a great development, consisting of no less 

 than from thirty to forty comma-shaped bags, packed closely 

 together within one envelope, as in Fig. 36. The digestive 

 cavity has undergone slight changes, the oesophagus has re- 

 mained as in previous stages, but we have a short intestine into 

 which the long stomach empties. When seen from above, the 

 head is pointed; seen in profile, it projects in a quadrangular 

 flap, and shows the rudimentary tentacles formed at the base 



