riS2 "ENDEAVOUR" SCIENTIFIC EESULTS. 



thus give rise to supplementary main fibres. The main fibres 

 are occupied by a stout core of loosely packed spicules, which 

 usually do not lie parallel to the axis of the fibre, but are in- 

 clined outwards from it at a small angle. As the extremitv of 

 the fibre is approached the spicules become more plumose in 

 the arrangement, and more and more free from enveloping 

 spongin and finally form a sheaf supporting, and to some 

 extent piercing, the dermal membrane. 1 he connecting fibres 

 are never aspiculous, though they often contain but a single 

 spicule. Acanthostyles occur in relatively small number 

 scattered within the fibres, through the intermediate tissues, 

 and as widely spaced echinating spicules. Smooth megas- 

 cleres scattered through the ground substance are moderately 

 abundant. This description of the main skeleton, as already 

 pointed out, has reference to the condition which is most 

 typical. In the type-specimen of T. ruhcns var. lamella, on 

 the other hand, there is an absence of any marked regularity 

 in the arrangement of the fibre-reticulation, the fibres are only 

 sparsely cored, and the smooth styli of the sponge interior 

 are on the whole notably smaller than in most other examples. 

 Still, the probability is that these differences are nothing more 

 than individual variations, and for the following reasons: — 

 (i.) The sponges are apparently identical in all other essential 

 respects, (ii.) The pattern of the main skeleton reticulation 

 and the degree of development of the spicule-core of the fibres 

 are sufficiently variable in all cases to render them untrust- 

 worthy as a basis for separation, (iii.) The size of the smooth 

 styli always varies considerably in any given specimen, and the 

 number of those which attain to the maximum size is also 

 variable and as a rule proportionately small, (iv.) The same 

 cause which accounts for the reduction in the size of the spi- 

 cules might very well be responsible also for their diminution 

 in number. 



The accounts which have hitherto been given of the spicules 

 are most incomplete, and in regard to their measurements 

 entirely misleading. Lendenfeld mentions, in addition to acan- 

 thostyles, stvli of one kind only, whilst Whitelegge recognises 

 two. There are, however, three kinds which, though connected 

 by intermediate forms, are clearly distinguishable by dif- 

 ferences of shape or of situation. Firstly, there are the 

 principal styli, which are predominatingly the spicules of the 

 fibre core, and occur onlv in relatively small number in the 

 ground substance; secondly, there are the auxiliary styli, 

 which constitute the horizontal spicules of the dermal skeleton, 

 which are, further, the most abundant megascleres of the 

 ground tissues, and which, to a small though rarely appre- 



