188 M. Sars on the Development of the Annelides. 
forms of the process of division or furcation durmg its metamor- 
phosis in the foetus. The young (fig. 21) are, when they have 
escaped from the egg, short, oval, cylindrical, of a lively grass- 
green colour, and have the centre of the body surrounded horizon- 
tally by a circle of cilia (dd), while the head (4) is remarkable from 
two kidney-shaped eyes of a bright red colour, which occupy the 
same position as in the young Polynoé: these young are hkewise 
without any articulated jomts. The anus (/) is more distinctly 
visible as a small round aperture at the posterior extremity of the 
body than in the young Polynoé. They swim very quickly about 
in the water by means of the cilia, and always towards the light. 
In short, they resemble so closely the young of the Polynoé, that 
there can scarcely be a doubt of their belonging to some Annelide. 
As I was unable to ascertain either the species to which these 
eges and young belonged or their further development, I must 
content myself at present with the mere announcement, that some 
sea-Annelides secrete their ova enveloped in a mucous mass of a 
certain form, as has long been known of the leech ; on the con- 
trary, others deposit free eggs *. 
EXPLANATION OF PLATE IV. FIGS. 12 To 21. 
Fig. 12. represents a Polynoé cirrata, natural size: a dorsal view. The yel- 
lowish gray mass, @ aa, which covers the back (with the exception 
of about the anterior fourth and below and between the branchiz), 
from which the young are on the point of escaping. 
Fig. 18. An egg taken from the cavity of the body, magnified and some- 
what compressed, to show Purkinje’s vesicle. 
Fig. 14. An egg taken from the back, showing the blackberry form of the 
yolk. 
Fig. 15. The same egg very much compressed, exhibiting a bright nucleus 
in each of the large granules (cells) of the yolk. 
Fig. 16,17. Further developed eggs, whose yolk or foetus is become smooth 
and whitish : a is the moveable fringe consisting of mucous fila- 
ments by which the eggs are connected. 
Fig. 18. The young animal just escaped, magnified and seen from the left 
side: a, mouth; 6, front, and ¢, posterior extremity of the body ; 
dd, circle of cilia; e, left eye. 
Fig. 19. A front view of the same animal: a, ventral surface ; dd, circle of 
cilia; ee, eyes. 
Fig. 20. represents the globular masses of eggs of an unknown Annelide of 
the natural size adhering to a piece of Zostera marina, cc: aa, the 
surrounding envelope of mucus; b 6, the eggs. 
Fig. 21. One of the young escaped from this mass of eggs: a dorsal view 
magnified: 5, anterior; ¢c, posterior extremity of the body; dd, 
circle of cilia; ee, eyes; f, tail. 
* For instance, the Nereides, as I have observed in Nereis pelagica and 
in a species of the genus Heteronereis Oersted. I saw in the month of 
March an immense number of eggs, which were very minute, globular, and 
of a beautiful azure-blue colour, deposited one by one by both of these An- 
nelides. 
