Development of the Marine Sponges. 391 



perpendicularly all over the body of the embryo, except at 

 its posterior or truncated end (fig. 13,/). 



This layer of monociliated cells is, as before stated, only- 

 represented generally in the embryo of Halisarca lobulams 

 (PI. XX. fig. 11), and omitted for convenience in the rest, or 

 rather reduced to a mere line of marginal dots. The cilia are 

 separated at the apex (fig. 13, c), and, from this, slope in op- 

 posite directions, more or less backward, to the posterior end, 

 which presents a group of large nucleated cells that are naked 

 or unciliated (fig. 13, d), as in Halichondria simulans. Lastly, 

 there is a brownish-yellow-coloured globular cavity in the 

 centre (fig. 13, e). The embryo progresses in the direction of 

 the apex, with the truncated end behind, and rotates from left 

 to right, as shown by the arrows respectively on the figure of. 

 the embryo of Halichondria simidans, attaching itself in the 

 same way to the bottom of the glass or foreign objects by the 

 bunch of large cells at the posterior end, which, thus evi- 

 dencing signs of being polymorphic and prehensile, I have 

 regarded as a temporary development for rooting or fixation. 

 At this time its total length is about l-360th inch, with a 

 little less transverse diameter, thus contrasting strongly, in 

 point of size, with the embryo of Halichondria simulans, 

 which, as before stated, is l-30th inch long by l-90th inch 

 wide. Such is the embryo of Grantia compressa Avhen it 

 has issued naturally from the parent after the manner men- 

 tioned. 



If we now compress this embryo under a glass cover, in 

 order to examine its composition with a much higher com- 

 pound power, viz. that of |-inch focus, we shall observe that 

 the cavity in the centre assumes a conical truncated form 

 (fig. 14, a), that the body between this and the ectodermal 

 layer of cells is composed of sarcode charged with cells which 

 are double the size of the latter, viz. 1 -6000th inch in diameter 

 (fig. 14, h), together with granules, and that the root-cells, each 

 of which is charged with granular plasma, including a distinct 

 nucleus and nucleolus, are again five times as large as the body- 

 cells — that is, 5-6000ths inch in diameter (fig. 14, c). But as 

 yet, although the embryo is matured and has left the parent, 

 there is not the least trace of spicules (fig. 14). 



Lieberkuhn (Archiv f. Anat. u. Phys. 1859, p. 379, pi. ix. 

 fig. 7), in describing and figuring this embryo with the cells 

 above mentioned, alludes to the brown (braune) colouring- 

 matter about the central cavity. 



In a still more advanced state, probably, this cavity appears 

 to become elongated and elliptical (fig. 15, a); and it is worthy 

 of remark that, while the brown colouring-matter seen about 



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