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 sae 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 line 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." 
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 coenosarcal 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. 06’ The 
same, with the thread protruded. 
c, d, e Successive stages in the development of the smaller form of 
nematocyst. 
Fig. 10. Section through a portion of a male gonophore sae of Astylus subviridis, 
showing various stages in the development of spermatozoa (cf. Pl. VIII. GQ). 
S. Wall of the gonophore sac, a reflection of the ectoderm. 
8’. Reflection of the same over one of the lobules of the generative 
mass. 
8”. Thin membrane enclosing the spermatozoa within the lobule. 
' N.B.—By error in plate marked x 100 instead of x 600. 
