264 



•ENDEAVOUR" SCIENTIFIC RESULTS. 



the EctyoninjE and the AxinelHda?, so that it might, with 

 almost equal justice, be placed in either group." 



The principal megascleres are slightly differentiated (but are 

 not separable) into two kinds as regards size, though not to 

 any appreciable extent as regards shape. The larger — which 

 are the less numerous — occur chiefly as coring spicules in the 

 excurrent or secondary fibres and as longitudinally directed 

 interstitial spicules in the mesial region of the sponge. Quasi- 

 echinating spicules are most commonly met with in connection 

 with the secondary fibres and their connectives ; the frequency 

 of their occurrence varies greatly in different specimens, and in 

 some they are comparatively rare. The auxiliary megascleres 

 (tylostvli) also vary in abundance, though they are never by 

 anv means scarce : they are, for the most part, scattered singly 

 and lie parallel to the fibres ; but parallel bundles — chiefly con- 

 fined to the mid-region of the lamina and longitudinally 

 disposed — also occur. 



The spicule characters are as follows : — 



(i.) The principal megascleres are straight to curved, grad- 

 ually tapering; styli, of very variable length in any given 

 specimen, and in different specimens differing to some extent 

 in regard to their precise form and maximum size. In the 

 specimen from which the spicules shown in the text figure 

 were drawn, and in a mounted slide prepared from a piece of a 

 British Museum specimen labelled EcJiinoclatliria tenuis, they 

 almost invariably exhibit a handle-like basal part (suggestive 

 of the handle of an oar), about 10 to 20 n in length, which may 

 or may not expand slightly at the end of the spicule to form a 

 faint basal knob. In some specimens obtained by the "En- 

 deavour," on the other hand, the .spicules approach very 

 closely in form those of O. inornata, sp. nov. (text-fig. 57), 

 and only a small proportion of them are marked by a "handle" 

 which, even so, is usually not well defined. In the first- 

 mentioned specimen, in which these spicules are of slenderer 

 proportions than in any of the others, they range from about 

 70 to 280 (but are very seldom more than 240) \i in length, and 

 are at most 8 j^ in diameter; w^hilst in the last-mentioned speci- 

 mens, in which their size is greatest, they range in length from 

 80 to 310 /I and attain a maximum diameter of 12 \i. The 

 largest spicules are mostly to be found amongst those which 

 project at the surface. Oxeote modifications, which appear 

 to be always of lesser than the medium length, are of oc- 

 casional occurrence. Usually, amongst the shorter spicules 

 (of length below, say, 130 ]i) there are some with a few (seldom 

 more than one or two) spine-like prominences ; these (vestigi- 

 ally spined?) spicules appear to occur most frequently in 



