PORIFERA. III. 



59 



without projecting spicules, but it is densely beset with low wart-shaped papillae, which may vary 

 somewhat in height and therefore be more or less conspicuous. The dermal membrane is a thin, but 

 somewhat solid membrane; it is densely charged with chelae. Oscula and pores: The mentioned 

 papillae are, I suppose, both oscular and pore-papillae, the fact is that there seems to be some difference 

 in their structure; some of them are relatively pointed and have an opening above, while most of 

 them are broader above and have here a prominent edge, but inside this are closed by a membrane; 

 in this membrane I have not observed pores, but probably they are closed; in both cases there are 

 large, hollow spaces below the papillae. 



The skeleton. The dermal skeleton; as the skeleton formed of the acanthostyli is quite in- 

 considerable, it is the skeleton consisting of the dermal spicules which forms by far the greatest part 

 of the whole skeleton; it consists of fibres which stretch quite from the base of the sponge upwards 

 and support the dermal membrane; the fibres run more or less vertical, outermost, at the surface, the 

 spicules are somewhat penicillately spread, or the fibres bend off below the membrane and run 

 under it as horizontal fibres. The fibres may have a rather variable thickness, but they are always 

 relatively thick and consist of many spicules; the thickness was e. g. measured to o-o6— 0*24 n,n '. 

 Under their course outwards the fibres may be more or less branched. In the wall of the papillae 

 the dermal spicules form a dense skeleton, King parallel with one end towards the edge of the 

 papilla and here they are somewhat projecting. The dermal membrane itself is densely charged 

 with chelae, forming a dense layer. The main skeleton consists as commonly of acanthostyli with 

 their head-ends attached to the substratum; the skeleton is much dispersed as there is only found a 

 bundle of styles in each place where the fibres, formed of the dermal spicules, go down to the sub- 

 stratum, the styli thus forming the lowermost part of these fibres, just at the substratum. At the 

 base a somewhat rich amount of spongin is found, in which the heads of the acanthostyli are imbedded. 



Spicula: a. Megasclera. 1. The skeletal spicules are straight or, especially the larger ones, 



slightly curved acanthostyli; they taper into a long apex, which in the larger of them is a little more 



abruptlv pointed outermost. The head may be somewhat various, it is generally not much swollen, but 



however somewhat pronounced on account of its spinulation. The spines are largest on the head; the 



larger styli are only spined below, when they are shorter the spinulation goes further out, and the 



smallest styli are entirely spined; in these latter the spines are rather large and they are reclined, in 



the larger styli the spines are most often smaller and less distinctly reclined. The length varies much, 



from 0-095— 0-62 mm , and the diameter of the head from 0-014 — 0-039 mm . Ah 1 transitions in size are found, 



but the intermediate sizes are rare. 2. The dermal spicules are long, straight or very slightly 



curved strongyla which are of the same or about the same thickness in the whole length; one end 



is short and rounded, the other is a little longer, nearly truncately pointed, this latter end is generally 



slightly swollen, not so much however that the spicule may be termed a tylostrongyle; the swollen 



end corresponds to the original end of the spicule; sometimes both ends may be very slightly swollen, 



the spicule thus approaching a tylote; the strongyla may be quite slightly polytylote. The length is 



0-37— 0-52 "'"' and the diameter about 0-004— o-oo8 mm . Quite monactiual developmental stages were 



found, b. Microsclera; these are chelae arcuatae, they are of ordinary shape, with a regularly and 



evenly curved shaft, the tooth is elliptical and the alae lobe-shaped, short and rounded, and of the 



8* 



