and the Embryology of Aulolytus cornutus. 393 



those rings the dorsal cirri gradually increase in length, 

 reach their maximum about the middle of the body, and 

 then diminish again in the same ratio towards the tail, 

 where they are hardly perceptible. The rings following 

 the six rings, with dorsal cirri of the same length, differ 

 m many respects from them. In the former there are 

 two bunches of bristles, the dorsal made up of long, thin, 

 needle-like bristles (PI. IX., fig. 5), supported by a tubercle 

 (fig. 4, A'), which are not retractile, and a ventral cluster 

 (fig. 4, h) made up of shorter, stout bristles (PL IX., fig. 6). 

 They are composed of two joints, the smaller exterior 

 joint having the shape of a claw. The ventral bristles 

 are retractile, and easily movable. These long, needle- 

 shaped bristles are wanting in the anterior rings, which 

 are not provided with a dorsal tubercle (see PL IX., fig. 3), 

 and have only a ventral tubercle supporting the short, 

 stout, retractile bristles like those of the posterior rings. 



The eggs, in their earlier stages of development, are 

 found thickly packed between the walls of the alimentary 

 canal and the outer wall, on each side of the body for its 

 whole length. The eggs, however, do not attain their ma- 

 turity in the cavity of the body. As they develop, and fill 

 more and more the space between the wall and the alimen- 

 tary canal, some of them even finding their way into the 

 dorsal cirri, there is developed on the lower side of the 

 body a large bag, into which they pass. This pouch ex- 

 tends from the 12th to the 25th or 26th ring when fully 

 swollen with eggs ; it has an elliptical shape (PL IX., fig. 2), 

 with a slightly wavy outline, the length of the smaller 

 axis of this ellipse being about three times the breadth of 

 the body. In this bag, which communicates freely with 

 the cavity in which the eggs are formed, the eggs come to 

 maturity; and soon after the young embryos have been 

 hatched from the eggs, the envelope of the pouch bursts, 

 and the young are left to swim freely about. 



JOUKNAL B. S. N. H. 50 JULY, 1862. 



