220 THE VOYAGE OF H.M.S. CHALLENGER. 



S. Digestive cavity of tbe zooid lined with elongate gastric cells. 



M. Longitudinal muscular layer of the zooid. As in Astylus subviridis, numerous 

 canals pass off from the margin of the rounded base of the zooid, but none 

 from the under surface of base itself. 



D Z, D Z. Dactylozooids. 



P. P. Mouths of the sacs of the dactylozooids. 



L, L. Peculiar protective laniime, or lids, folded in this genus in front of the openings 

 of the cyclo-systems. In the case of the left-hand system of the figure the 

 ramifications of the superficial network of the ccenosarc, prolonged into the 

 body of the lid, are shown, and also the nematophores with which the lid 

 is provided. In the other system represented, the superficial layer of the 

 ccenosarc is shown intact. The downward prolongation of the base of the lid 

 which should pass between the sac of the gastrozooid and its main 

 upward canals, is omitted for clearness' sake. 



N, N. Nematophores. One of these is situate at tbe outer margin of the cyclo-system 

 in each interval between the sacs of the dactylozooids. 



G. Female gonophore contained, with two others in earlier stages, in a special brood-sac 

 as yet not far advanced in development. 



G'. Brood-sac in full development containing ova and embryos in all stages of develop- 

 ment. 



Ov, Ov'. Fertilised ova in advancing stages of development and cell multiplication. 



P 1. Early stages of planula embryo. The thin ectoderm appears as just differentiated. 



P 2. Planula fully advanced with more fully developed and thickened ectoderm. 



P 3. Fully developed planula with highly differentiated ectoderm containing nemato- 

 cysts, &c. 



PLATE X. 



Shows certain details of structure of the soft parts of Sporadopora dichotoma and of 

 Astylus subviridis. 



Fig. 1. Section transverse to the longitudinal axis of a gastrozooid of Sporadopora 

 dichotoma, taken at a point above the junction of the tentacles with the 

 body of the zooid. Hence the tentacles appear in this section as isolated 

 structures. 



S. Digestive cavity. 

 G. Large gastric cells with their nuclei. 



M. Muscular layer and basement membrane at this region of the zooid 

 comparatively little developed. Shows longitudinal fibres cut across. 



