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



Fig. 5. Section transverse to the axis of the zooid of a segment of the body wall of a 

 gastrozooid of Sporadopora dichotoma, taken near the lower region of 

 the zooid. 



S. Wall of the sac of the zooid seen in section. 



E. Ectoderm. 



M. Muscular and basement layer showing a series of stout longitudinal 



slips in section. 

 L. Layer of transparent endodermal cells, the representatives in this 

 region of the larger elongate gastric cells which exists higher up in 

 the body cavity. 

 EN. Pigmented endoderm cells, such as hue the canals of the 

 ccenosarcal meshwork. 

 Fig. 6. Portion of the muscular layer of the body wall of a gastrozooid of Sporadopora 

 dichotoma viewed from its inner surface. The layer is seen to be composed 

 of a closely set series of longitudinal narrow muscular slips. The layer is 

 crossed by fine transverse striations, the nature of which was not deter- 

 mined, no definite circular muscular fibres having been detected in the 

 zooids. The striations probably are caused by wrinkles in the basement 

 membrane. 

 Fig. 7. One of the longitudinal muscular slips of the last figure, much enlarged, to 



show that it is composed of fusiform nucleate closely-packed elements. 1 

 Fig. 8. These fusiform muscular elements still more magnified. 

 Fig. 9. Nematocysts of Sporadopora dichotoma. 



a Elongate form of nematocysts occurring only in the nematophores 

 and surface layer of the ectoderm, and that investing the more 

 superficial ccenosarcal canals, a' The same, with the thread pro- 

 truded. 

 b Smaller form of nematocyst, abundant in the tentacles of the gastro- 

 zooids, ectoderm of the dactylozooids, and other regions. V The 

 same, with the thread protruded, 

 c, (7, e Successive stages in the development of the smaller form of 

 nematocyst. 

 Fig. 10. Section through a portion of a male gonophore sac of Astylus subviridis, 

 showing various stages in the development of spermatozoa (cf. PI. VIII. G). 

 S. AVall of the gonophore sac, a reflection of the ectoderm. 

 S'. Reflection of the same over one of the lobules of the generative 



mass. 

 S". Thin membrane enclosing the spermatozoa within the lobule. 



1 N.B. — By error in plate marked x 100 instead of x 600. 



