On the Young Stages of a few Annelids. 331 



ance, they spread fan-like in every direction, roll themselves 

 up in a ball like a hedge-hog, and become quite motionless, 

 but soon start off again on their rapid gyrations, performed 

 by means of an exceedingly powerful circle of vibratile cilia 

 surrounding the head. The body at this early stage consists 

 of seven distinct rings, and faint indications of a couple more 

 in front of the anal ring, also surrounded by strong vibratile 

 cilia. The dorsal cirri are slight swellings, and at the brse of 

 each we find two brushes of permanent bristles, the one com- 

 posed of serrated, file-like, rough bristles (Fig. 42 a ), similar to 

 those observed by Claparede in an unknown Annelid larva,* 

 the other, of smooth setse, like those of the adult, placed im- 

 mediately at the base of the rudimentary dorsal cirrus. The 

 oesophagus and stomach are separated by a slight constric- 

 tion ; the younger stages (Fig. 39) have no pigment cells, and 

 are moderately transparent ; there are six eyes, the two larger 

 ones, placed nearer the sides of the body, soon disappearing. 

 In subsequent stages the body lengthens and becomes more 

 pointed ; pigment spots appear near the head, extending 

 towards the anal ring ; they resemble those of Polydora, pass 

 through the same stages, and before they disappear, have lost 

 their beautiful star-shaped form, making a double row of more 

 or less rectangular spots as in Fig. 40. The changes have been 

 principally in proportions, the tentacles have slightly de- 

 veloped, the large anterior brush of serrated bristles losing its 

 prominence. The dorsal cirri, as well as the tentacles, now de- 

 velop rapidly, the powerful circle of vibratile cilia round the 

 head having nearly disappeared, Fig. 41. We find in some of 

 the rings of the anterior part of the body the first appearance 

 of the clusters of stiff, hook shaped bristles, like those of Fig. 

 44, found with the lower brush of smooth bristles in the adult ; 

 the eyes are four in number, quite small, the pigment spots 

 have disappeared, as well as the anterior brush of temporary 

 bristles. The little worm now enters a stage when it rapidly 



* Clapauedk A. R. E. Beobachtungen. ... PL VI., Fig. 6. 



