46 



PORIFERA. II. 



Neither do I think, however, that the question is of a constant difference as to form; on the contrary 

 the fact of the long lateral branches being always thin and with few spicules, while the short ones 

 are thicker and with more spicules, leads to the supposition that the feature is due to contraction, 

 and I think that it must be explained in this way. An examination of a series of different individuals 

 tends absolutely in this direction, and thereby we get a natural explanation of the always constant 

 relation between the length and thickness of the branches. When the branches are long and thin 

 thev are slightly curved upward. As before mentioned they are placed along each of the narrow sides 

 of the axis, but thev are not arranged in any certain manner, and the distance between them may 

 be somewhat different. Two branches are often found beside each other on the same side, but then 

 thev are generally very close to each other, sometimes more or less coalesced; in other instances, 

 however, the distance between them is somewhat greater. Sometimes the branches are, even pretty 

 distinctly, placed in two rows on either side, and this structure is perhaps, strictly spoken, the most 

 common one; but when the rows are very close to each other and the single branches are not placed 

 directly opposite to each other, the feature is only seen indistinctly. When the branches are short, 

 those that are thus close to each other seem to coalesce to one branch, so that we get only one thick 

 spicula-bundle. At the upper end the branches become short and are turned upward, and they con- 

 tinue in a fan-shaped manner round this end. In the lower part of the sponge, towards or quite up 

 to the spot where the lateral branches begin, the stalk is surrounded by a more or less thick layer 

 densely packed with particular spicules, which layer will be more thoroughly mentioned under the 

 skeleton. This feature contributes to some degree to the thickening of the lower part. The stalk is 

 generally straight, but sometimes it, or especially its lower part, may be irregularly bent and cracked. 

 The largest specimen is of a length of ca. i8o mm , but it is broken below ; the part of it carrying lateral 

 branches is of a length of a little more than ioo mm . The specimen is very slender, the stalk in its 

 broadest part is only of a thickness of i — r5 mm , at the very base 2 mm . Some fragments of another 

 specimen, which I suppose to have been upon the whole a larger one, are more robust, the stalk in 

 its broadest part being 4 mm . All the specimens, as mentioned, are broken below, but to judge from 

 stalk-fragments in hand, the sponge may grow to a considerable length. Thus we have stalk-frag- 

 ments of a length of no mm , broken in both ends and carrying neither lateral branches nor root-like 

 off-shoots. The thickest stalk-fragments are of a diameter of 5— 6' nm . The smallest specimen, which 

 is likewise broken below, is of a length of 20 mm , and the stalk is o-t,™™ thick. The colour (in spirit 1 

 is white or yellowish white. The consistency is firm on account of the skeleton, but the sponge is 

 fragile. The surface of the stalk and the branches is smooth without any projecting spicules; in the 

 lower part of the stalk where the mentioned coating grows thicker, wrinkles and folds may be seen. 

 While the stalk is smooth, also in the places coated with the mentioned layer, the root-part and 

 especially the root-branches are shaggy, owing to the projecting of the needles of the coating layer. 

 No bounded dermal membrane is to be observed. Outermost in the axis a dense layer of spicules is 

 found belonging immediately to the skeleton of the axis. On the outside of the spicula-fibre of the 

 lateral branches a thin layer of tissue is found closely filled with microscleres, and the same layer 

 may also be found in the axis between the bases of the branches, as it may also be traced here and 

 there in other places of the axis, but it is not bounded outward as a membrane. Neither oscula nor 



