190 
the nephridia are sac-like, and their dorsal lip bears from 
two to five papille—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 65 mm. ‘Three of 
the specimens (4°6, 5-6 and 5°6 mm. in length) were ex- 
amined living. The following description is drawn from 
specimens 4°6 to 5°] mm. in length. Such examples are 
‘2 to'3 mm. in diameter and the chetigerous 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. 09). 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 lps 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 
