PORIFERA. II. 



145 



preserved to any greater extent, circular openings of a diameter of about o - 5 mm are found in it, also a 

 few smaller ones, and these openings must be regarded as oscula. In the thicker, irregularly leaf- 

 shaped specimens a few wide perpendicular canals are also often found, opening in the edge; but I 

 am not quite sure, whether the question is here of real oscular canals, or they are secondary canals 

 arisen by coalescing. In the membrane coating these canals, dermal spicules are found and also pore- 

 shaped openings; this, however, does not exclude the fact that they may belong to the original canal 

 system, and, on the other hand, in undamaged specimens their mouths are surrounded by the dermal 

 membrane as a round, sharply bounded opening. I therefore regard it as probable that the question 

 is of oscula, and the fact is then that the small oscula on the surfaces lead to the smaller, horizontal 

 canals, while the oscula found in the edge are larger and lead to longer perpendicular canals which 

 pass down through the thicker parts of the irregularly leaf-shaped sponge. 



The skeleton. The dermal skeleton, as mentioned above, consists chiefly of bundles of dermal 

 spicules, which are spread in a somewhat peuicillate way and support the dermal membrane, and, but 

 only to a slight degree, pierce it. This skeleton is otherwise little regular, the bundles are most 

 frequently more or less recumbent, often quite so, and scattered spicules may also be found in the 

 membrane; in some places the skeleton may be formed entirely of horizontal, scattered spicules, which 

 seems especially to be the case in places where no pores are found. The ridges of the surface are often 

 seen to be more spined, which is then owing to the fact that the spicules of the skeleton itself here 

 project through the dermal membrane; I suppose, however, that this feature is often due to damaging. 

 Tornotes are not found in the membranes of the canals, except in those of the above mentioned larger 

 longitudinal canals. The mail/ skeleton is a somewhat irregular, mostly polyspieular network. The meshes 

 are mainly quadrangular or rectangular, but may also be more irregular. The skeleton has otherwise 

 a similar structure as in many leaf-shaped Renierse and Chalininse, longitudinal fibres being found 

 running from the base up through the sponge, and bending to all sides towards the surface, accord- 

 ingly as well towards the two sides as towards the edges. Where the skeleton is most regular, these 

 fibres are running parallelly with a distance between them of about one spicule; the connecting transverse 

 spicules may be placed perpendicularly on the longitudinal fibres or more or less irregularly, and with 

 greater or smaller distance between them, but long secondary fibres are not found. The longitudinal 

 fibres ma}' reach a thickness of up to cri5 m,n , and have a considerable number of spicules alongside; 

 the transverse fibres, on the other hand, are single spicules or bundles of only few spicules. Often 

 the skeleton seems to be somewhat less regular. Spongin is distinctly present in the nodes of the 

 skeleton, but it is very clear; also in the longitudinal fibres it is found rather copiously. 



Spicitla: a. Megasclera. 1. The skeletal spicules are acanthostyli and acanthostrongyla 

 mixed in about equal numbers; they are straight or most frequently slightly curved with the curve 

 nearest to the basal end. The spinulation may be somewhat varying, sometimes it is rather dense, 

 sometimes more scattered, and almost quite smooth needles may be found singly. The spines are 

 most frequently rather coarse; at the upper end they are a little more close-set and generally some- 

 what larger. The styli have a sharp, middle long to rather long, point, which is oftenest smooth 

 through its whole extent. The strongyla are distinctly seen to be monactinal, being always broader 

 at one end than at the other, so that a distinction is always found between a basal end and an apical 



The In^olf-Expedition. VI, 2. Iq 



