from the North Sea. 87 



canal-system, which Prof. Schultze here describes ; and it is 

 difficult to explain the extraordinary circumstance that these 

 openings, which are so important to the life of the sponge, 

 should have their place where it is adherent to the rock, and 

 where the current issuing from them would meet with such 

 resistance. 



By an incision in the head (''the sponge") Prof. Schultze 

 laid open its inner structure. The stem (*'' the coil ") is con- 

 tinued, as in our sponge, deeply into it ; and the spicules of the 

 head, inserted among the larger ones of the axis in the form 

 of flattened strings or blades, are regularly disposed all round 

 '^ the axis." The figure (M. Schultze, ' Die Hyalonemen,' pi. 2. 

 f. 1) shows, though rather indistinctly, this structure, which 

 accords well with that of our sponge. The parenchyma of the 

 specimens examined by Prof. Schultze, was very much dimi- 

 nished by drying. 



It is evident that the stem (" the coil ") of all the specimens 

 of Hyalonema described has been torn off at its free end. 

 Professor Schultze expressly states that its long needles are 

 all broken ; they are of the same type of form as those of 

 our sponge — spindle-shaped, more or less round, thickest at 

 the middle, tapering towards both ends, and somewhat spirally 

 bent. The thickest part of many of the smaller and those of 

 middle size has an inflation or nodule, in the interior of which 

 the central canal gives ofl" two short transverse canals, at right 

 angles and in opposite directions. All this is as in our 

 Sponge. From this simple primary type of spicule a number 

 of secondary, more complicated forms are derived, almost 

 without exception the same as in our Sponge, although in the 

 latter not so fully developed. Such are the spicules with 

 graduated ends (/. c. pi. 3. f. 5, 6, 7, our figs. 24, 25) or studded 

 with short spines, into which the canal does not enter (/. c. pi. 3. 

 f. 1-4, 9-15, our fig. 26), or with branches in two or four 

 crossing directions {I. c. pi. 4. fig. 1, our figs. 14, 19) ; but 

 those of Hyalonema are strongly and perfectly developed, 

 forming six-rayed needles, or five-rayed ones where one part 

 of the primitive needle is lost {I, c. pi. 4. f. 3, 5, 6). There can 

 be a branch also in only one side (?. c. pi. 3. f. 15, to compare 

 with our figs. 15, 18). Whether the arcuated spicules without 

 noduks, found in the dermal layer of our sponge (figs. 6, 35), 

 are to be recognized in the spicules figured by Prof. Schultze 

 (pi. 3. f. 2, 3) may be left undecided. 



Besides these affinities, there are also differences. In addi- 

 tion to the spindle-shaped needles, Hyalonema has also another 

 type of siliceous spicules, which are not to be found in the 

 specimens of our sponge I have examined. It is the type of 



