47 



rugae, especially conspicuous towards the top of the jjrocess (PI. V, fig. i and 4); these rugae 

 correspond to those we saw in 1365 (PI. V, fig. 11). In the transverse section (tig. 2) the central 

 canal is seen to be surrounded by narrower canals some of which are often still rather wide-, in 

 addition to these canals nnmerous very narrow ones are just perceptible to the naked eye. I find 

 this arrangement likewise very conspicuous in some specimens of a S. vagabundci\ more especially 

 in B. M. 17 and B. M. 19 Exactly like we found it in 1365 the central canal shows openings 

 in its wall, by which there is communication with other canals. Soundings and series of sections 

 prove, that at least some of the main peripheral canals communicate with the central one as 

 is shown by the arrows in fig. 1. The larger canals can be foliowed almost through the whole 

 length of the process and come very near to the base of it. A remarkable feature of these 

 specimens is that their lumen generally increases towards the lower parts, the external aperture 

 on the top being very small in comparison to the diameter of the canal say half way the 

 process. Microscopical sections of such specimens teach us how much space is taken by these 

 main canals (PI. V, figs. 12 and 13). The chief difference between such sections and those of 

 1365 lies in the fact that the larger peripheral canals in the former may reach a greater diameter 

 than in the latter as is easily seen by comparing figs. 13 and 19. 



A similar longitudinal section through a typical example of tropus pyramtdalis, e g. 

 426 a (PI- V, fig. 3) shows, mutatis mutandis, the same. Again we find a wide central canal, 

 diminishing in lumen towards the top. Next to this main canal are others, narrower but still 

 comparatively wide, running more or less parallel to the central one and in direct communication 

 with it. The structure of the wall with its rugae is like in 948 g. 



In fig. 2 on PI. IV I give an illustration of the longitudinal section of an example of 

 tropus concrescens (3050). Here we see two central canals of about the same diameter (a third 

 one is present in the other moiety). It is clearly seen that the diameter is again decreasing 

 towards the top and the concentric rugae are present like in 948b, 948 g, 426a etc. Whereas 

 in 948 g the central canal opens at the top of a process with a small aperture, which is, however, 

 distinctly visible to the naked eye no such apertures are to be seen in 305c!. Here the main 

 canals are formed by confluence of a few narrower ones, as is shown in fig. 2 (PI. IV) on the 

 left hand side. In 305 a we have a specimen consisting of several processes partly fused at 

 the top. A longitudinal section through one of the "clubs" shows, that several narrow canals 

 are confluent till two main central canals are formed, which afterwards fuse again (PI. V, fig. 5). 

 Transverse sections through the stem (PI. V, fig. 20) show us the now single central canal (a), 

 lined by soft transparent tissue, ancl some narrower canals (ó) around it. The section strongly 

 reminds us of what we saw in 1365 (PI. V, fig. 19). 



In more massive specimens of tropus glacbosa, like e. g. 931 b (PI. V, fig. 6) we see 

 fundamentaly the same as in 305 a and 305 c!; the canals marked with arrows 1, 2 and 3 

 correspond to the main central canals of the above mentioned specimens. They possess the 

 same structure and are likewise formed by confluence of some smaller canals. In a still more 

 massive specimen of the same tropus, viz. 612 a (PI. IV, fig. 9) similar longitudinal canals are 

 visible ; they are, however, narrower, compared to the diameter of the whole sponge and there 

 is more soft tissue around the lumen. 



