PORIFERA. II. 47 



pores have been observed. From the arrangement of the skeleton it was to be expected that the 

 pores might be found on the narrow sides of the axis between the branches, but here none were dis- 

 covered. The possibility is perhaps not to be excluded that the lateral branches may act as oscula, 

 in which case it would have to be supposed that in their most extended state they are hollow and 

 connected with the canals of the stalk mentioned below under the skeleton; such a thing, however, 

 has not been observed 1 ). 



The skeleton consists in the axis of parallel needles, closely connected with each other, and 

 with the points turned toward the upper end of the sponge; accordingly the axis is firm and hard. 

 It is, however, not massive, but pierced, throughout its length, by a number of canals separated by 

 close-spiculed parts, and the whole structure is outmost surrounded by a close-spiculed layer. All the 

 spicules are parallel to the longitudinal axis of the stalk. It is no easy thing to get a clear view of 

 the number and arrangement of the canals, as whole transverse sections of the hard stalk are only to 

 be obtained with great difficulty. There are always two rather large canals, one along the middle of 

 either broad side of the axis; then the rule seems to be that on each side of these canals two small 

 ones are found occupving, accordingly, the corner parts of the stalk; thus we have altogether ten 

 canals, but sometimes there seem to be still more. Down in the stalk the structure is about the 

 same, and the two chief canals may generally be recognized, but most frequently there seem here to 

 be fewer canals and less regularity. In the thickened parts at the base of the stalk many more 

 canals and more irregular ones are seen. To judge from observations on the few root-fragments in 

 hand, the canals would seem also to pass into the root-branches. The stalk is sometimes a little 

 twisted in the lower part, and then the canals follow the winding always following the longitudinal 

 direction of the spicules. The skeleton of the branches consists of an axis, which may be more or less 

 thick in proportion to the length of the branch, and is constructed of parallel spicules with their end 

 turned outward; it is inserted in the narrow sides of the principal axis between the longitudinally 

 running spicules of this axis in such a way, that the spicules of two lateral branches placed opposite 

 to each other meet in the middle, and the spicules inserted in the principal axis are spread in a fan- 

 shaped way in the longitudinal direction of this axis. As more thoroughly mentioned below under 

 the spicules, the skeleton of the axis consists of styli with an admixture of subtylostyli especially in 

 the outer part, while the skeleton of the branches consists of subtylostyli. The outside of the axis is, 

 in its lower part, coated with a layer of varying thickness. It is rather firm and compact, showing a 

 smooth surface with here and there some wrinkles and folds. It reaches towards, or almost quite up 

 to the place where the lateral branches begin. It may be of varying thickness, from a scarcely per- 

 ceptible crust to a rather considerable layer, the thickness being greatest towards the base, but also 



') With regard to all the symmetrical, branched J/yra/t'-species — i.e. the genus Asbeslopluma — it is a fact that 

 neither pores nor oscula have ever been mentioned in the literature. Either they are not mentioned at all, or it is stated 

 that thev have not been found. Now several things might indicate that this fact with regard to some species is caused by 

 the dermal membrane generallv being absent on the material obtained for examination. The specimens sometimes show 

 ruined remains of a membranous character, especially at the base of the branches. With regard to the present species it is, 

 perhaps, not improbable, that in the undamaged sponge the dermal membrane is, to a higher or smaller degree, suspended over 

 the lateral branches, so that these are only partly free, and then pores and oscula are presumably found in this membrane. It 

 is obvious that such a suspended thin membrane is easily destroyed, as the sponges in question is upon the whole from 

 great depths and may be damaged in the trawl, or to a still higher degree in the swabs, with which instruments most of 

 the individuals of the Ingolf-Expedition have been obtained. 



