188 M. Sars on the Development of the Annelides. 



forms of the process of division or furcation during its metamor- 

 phosis in the foetus. The young (fig. 21) are, when they have 

 escaped from the egg, short, oval, cyHndrical, of a Hvely grass- 

 green colour, and have the centre of the body surrounded horizon- 

 tally by a circle of cilia {dd), while the head [b) is remarkable from 

 two kidney-shaped eyes of a bright red colour, which occupy the 

 same position as in the young Polynoe : these young are likewise 

 without any articulated joints. The anus (/) is more distinctly 

 visible as a small round aperture at the posterior extremity of the 

 body than in the young Polynoe. 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 Polynoe, 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 

 eggs 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 Polynoe cirrafa, natural size : a dorsal view. The yel- 

 lowish gray mass, a a a, which covers the back (with the exception 

 of about the anterior fourth and below and between the branchiae), 

 from which the young are on the point of escaping. 



Fig. 13. 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 ; b, front, and c, posterior extremity of the body ; 

 d d, circle of cilia ; e, left eye. 



Fig. 19. A front view of the same animal: a, ventral surface ; dd, circle of 

 cilia ; e e, eyes. 



Fig. 20. represents the globular masses of eggs of an unknown Annelide of 

 the natural size adhering to a piece oi Zoster a 7narina, cc: a a, the 

 surrounding envelope of mucus ; b b, the eggs. 



Fig. 21. One of the young escaped from this mass of eggs: a dorsal view 

 magnified: 6, anterior; c, posterior extremity of the body; dd^ 

 circle of cilia ; e e, eyes ; /, 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. 



