53 



compare such a section with one of a specimen the lumen of the central canal of which is 

 half way diminished by partial contraction of the concentric muscle cells. (PI. VI, fig. 9). Here 

 the meshes are likewise elongated, but now the long axis is perpendicular on the axis of the 

 canal lumen. Between these extremes we find cases that the parenchyma is in normal condition, 

 i. e. not under the influence of pulling- muscles. Consequently the meshes will not show a 

 markedly long axis as is to be seen in fig. 8 on PI. VI. 



If we compare this remarkable tissue with tissues of which the histological structure is 

 known, it comes nearest to the socalled adenoid or reticular connective tissue, as was first 

 suggested to me by my friend Pekelharing. After the studies of Bizzozero and Ranvier tin- 

 tissue of lymph glands and similar structures, is composed of collagenous fibres with flat 

 membraneous cells, forming very thin membraneous processes. Between these numerous other 

 cells, in casu lymphocytes, are situated. In the tissue described above we find exactly the same; 

 only the membraneous cells are a good deal larger. My sponges are preserved in strong alcohol 

 and I could not try various methods of fixation and maceration. I feel, however, some right 

 in applying the statements of histologists on the tissue of Spirastrclla by comparing sections 

 of, say, lymph glands with those of the sponge under consideration. It is true that I have not 

 been able to isolate the elements and so I cannot prove that collagenous fibres occur. But I 

 am almost sure not to be mistaken, if I declare fine threads on and between the flat cells to 

 be connective tissue fibres. In some places I believe the fibres to be more numerous ; such 

 places are seen as darker spots, owing to the greater quantity of fibres. Of course the fibres 

 clo not stain darker, but they fill the meshes and consequently the whole looks darker. Such 

 is e. g. the case at the periphery and arround and between the bundies of tylostyles. The 

 difference between the tissue in such places and that in others is exactly like the difference in 

 tissue of the fibrous capsula of a lymph gland and the tissue itself. 



In preparations stained with acid fuchsin there are always more "fibres" to be seen than 

 in those with some ordinary nucleus-stain. This is of course an argument in favour of the 

 fibrous nature ; if these were folds or thread-like processes of cells there would be no explanation 

 for the phenomenon. At any rate it is a connective tissue with very little intercellular substance. 

 It gives the impression of the large membraneous cells forming a sort of syncytium ; at least 

 I was unable to see separations, unless a transverse line I once observed, is to be explained 

 as a line of demarcation. Not having living material at my disposal I could not try to produce 

 such lines by silver nitrate, as Ranvier has done for the cells of the lymph glands. In acldition 

 to these flat cells, other cells occur, e. g. amoebocytes, myocytes, pigment-cells, scleroblasts etc. 

 Some of these cells are illustrated in figs. 9 and 10 on PI. VI. Whereas such cells are dispersed 

 throughout the whole parenchyma others are localised, forming long fusiform strings as can 

 be seen in every longitudinal section (PI. VI, fig. 5 d) ; they appear in transverse sections as 

 more or less rounded clustres (PI. VI, figs. 6 and jd). The fusiform strings are generally found 

 in connection with the main bundles of tylostyles. The nuclei of these large cells have an 

 ellipsoid shape and stain darkly ; therefore and because of their appearance in groups, packed 

 closely together these Mark cells" are easily seen even with low power. The shape of the cell 

 is somewhat elongated, with the long axis parallel to the long axis of the group. In sections 



