Development of the Marine Sponges. 399 



ciliated ectoderm (fig. 11, a), whose cilia in the anterior two 

 thirds (fig. 11, b) are much longer than those of the posterior 

 one, and, although still somewhat inclined backwards, stand out 

 from the surface in a bristly form (much like the cilia on some 

 of the embryos of the calcareous sponges), contrasting strongly 

 with those which cover the posterior third (fig. 11, c), which, on 

 the other hand, appear much shorter, or, at all events, are much 

 more inclined backwards, and thus lie closer together, ending 

 in a kind of tuft a little longer than the rest, where they meet 

 each other from opposite directions at the posterior extremity 

 of the body (fig. 11, d). The embryo is now coloured red- 

 violet, like that of the spongozoa in the parent, but most 

 strongly over the posterior third, where the colour-margin 

 appears to be somewhat pressed inwards laterally, and thus, 

 by its form and deeper colour, distinctly marks this portion. 



The other figure (12) represents another embryo (of which 

 there were forty or fifty swimming about the glass in which 

 the parent sponge was placed, for nearly a fortnight), of the 

 same kind as the foregoing, but with a papillary eminence on 

 the anterior extremity separating the cilia in front (fig. 12, b), 

 and a group of large tmeiliated cells projecting from behind 

 in the midst of the "tuft" of longer cilia just mentioned 

 (fig. 12, c). By lowering the focus, these cells were observed 

 to be part of a group filling the centre of the embryo (fig. 12, d) 1 

 after the manner of those presented by the earlier stages of the 

 embryo of the calcareous sponges, and indicating in the same 

 way the existence of a body-substance between them and the 

 ectodermal layer. Like the embryos of the other sponges, these 

 swim with the pointed end foremost and present a rotatory 

 motion from left to right, indicating, as before stated, that 

 the cilia are arranged over the body in a spiral direction. Of 

 course such cilia always lie, as before stated, in the opposite 

 direction to the progress of the body of which they are the 

 locomotive organs — that is, backwards. 



All the embryos had left the parent naturally, and averaged 

 in size about 16 by 10-1800ths inch in their greatest diameters, 

 or about 1-1 12th inch long — therefore much smaller than the 

 embryo of HalieJwndria simtdans, and much larger than that 

 of Grantia compressa. The most remarkable feature about 

 them is their deep red-violet colour ; and although they re- 

 mained alive and active for several days, as before stated, and 

 I placed objects in the glass vessel for them to become fixed 

 upon, this was not successful even in a single instance ; hence I 

 had not the opportunity of following their further development 

 as in Halichondria simulans. 



