270 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the nephridia are sac-like, and their dorsal lip bears from 

 two to five papillae — in fact these worms are miniature 

 copies of adults. Other specimens up to 44 mm. in length 

 were found at the same time and place which show a 

 similar condition of the prostomium and nephridia 

 (fig. 25), and are probably but little older than those 

 17 mm. long. It is probable that these specimens were 

 produced from eggs laid in the early spring of the same 

 year, so that the young worms are three or four 

 months old. 



I have examined seventeen post-larval stages of A. 

 marina varying in length from 3'5 to 6"5 mm. Three of 

 the specimen^ (4"6, 3"6 and 3'6 mm. in length) were ex- 

 amined living. The following description is drawn from 

 specimens 4"6 to 5*1 mm. in length. Such examples are 

 •2 to "3 mm. in diameter and the chretigerous portion of the 

 worm is nearly three times as long as the tail. 



The prostomium is a moderately large and somewhat 

 lozenge-shaped or spatulate structure at the anterior end 

 overhanging the mouth (figs. 57, 58). Upon it are seen 

 the eyes to the number of two to five on each side of the 

 middle line (figs. 56, 59). One of these, the oldest, is 

 larger than the rest. Their structure is described above. 

 The epithelium of the prostomium bears small scattered 

 groups of sense hairs (fig. 59). Immediately behind the 

 prostomium is the nuchal groove, the degree of develop- 

 ment of which seems to vary in different specimens. In 

 some it is scarcely recognisable, but in others it is a well- 

 marked groove extending across the posterior border of 

 the prostomium. When the lips of the groove are 

 everted the rapid movement of the cilia may be observed. 



Behind this is the peristomium in which the otocysts 

 are well seen (fig. 57). The internal diameter of these 

 organs is about '04 to - 06 mm., and the external aperture 



