404 Mr. H. J. Carter on the 



Fig. 12. The same, embryo more advanced : a, ectodermal layer ; b, pa- 

 pillary projection at the anterior extremity ; c, group of root- 

 cells at the posterior extremity, produced from d, the same kind 

 of cells in the centre of the embryo. 



Fig. 13. Grantia compressa, embryo as it issues from the parent. Assumed 

 vertical section, showing : a, the conical form of its body ; 



b, monociliated ectoderm ; c, opposite direction of the cilia at 

 the apex ; d, group of root-cells at the posterior extremity ; 

 e, central cavity ; f, line indicating the inner boundaiy of the 

 crust of monociliated cells on the surface, or ectoderm. 



Fig. 14. The same, embryo under pressure of a glass-cover, showing 

 the same as the foregoing, but with : — a, a conical truncated 

 form of the central cavity ; b, specimen of cells and granules 

 of the body between the central cavity and the ectoderm, 

 magnified on a larger scale, viz. l-24th to 1-UOOOth of an inch ; 

 and c, specimen of the root-cell on the same scale, showing 

 the nucleus and nucleolus. 



Fig. 15. The same, embryo slightly more advanced (?). Assumed verti- 

 cal section, showing the same as fig. 12, but with the central 

 cavity («) larger and elliptical in shape. 



Fig. 1G. The same, embryo at the commencement of the Fourth Period 

 of development, after it has become fixed, the cilia withdrawn, 

 and a few of the triradiate spicules have been formed : a, dermal 

 membrane or ectoderm ; b, triradiate spicules ; c, sarcode charged 

 with cells and granules, filling the interior. 



Fig. 17. The same, embryo more advanced, where the triradiate spi- 

 cules have increased in number and the club-shaped surface- 

 spicules have begun to appear and push outward the dermal 

 membrane : a, dermal membrane or ectoderm ; b, triradiate 

 spicules ; c c, club-shaped surface-spicules ; d d, sarcode charged 

 with cells and granules; e, specimen of the <l cells " of the body 

 on a larger scale, showing that they are spongozoa, and come 

 from fragments of the ampullaceoussacs ; f, monociliated spongo- 

 zoon ; g, spongozoa putting forth pseudopodial processes. 



Fig. 18. Young individual of Grantia compressa only a little larger than 

 the embryo from which it has been developed : a, body ; b, tri- 

 radiate spicules ; c, club-shaped surface-spicules. 



Fig. 19. Young individual of Grantia compressa taken from a branch 

 of Ptilota sericea, on which old and young specimens abounded : 

 a, b, c, the same as before ; d, foreign body to which it is at- 

 tached. 



Fig. 20. Magnified view of the club-shaped or characteristic form of 

 surface-spicule of the same, to show its form in figs. 18 & 19. 



Plate XXI. 



Fig. 21. Halichondria simtdans, Johnston, active locomotive embryo on 

 issuing from the parent naturally : a, body ; b, spicules, cells, 

 and granules with which the sarcode of the body is charged ; 



c, cells with cellulse in their interior, either undergoing endo- 

 genous cell-formation or foreshadowing the ampullaceous sacs ; 



d, monociliated layer of ectodermal cells; e, papillary projection 

 at the anterior extremity of the body not covered with cilia ; 

 /, root-cells forming a brownish-yellow ring round the truncated 



or posterior end, also not covered with cilia ; g, ring of large 

 long cilia along the line of demarcation between the root-cells 

 and the body : />, arrow showing the direction in which the 



