REPORT ON THE TETRACTINELLIDA. 
XXXIX 
Euspongia, this tissue in some species suffers a marked change in the neighbourhood 
of the flagellated chambers, granules appear in it, and are sometimes so richly developed 
as to obscure the collencytes. This modification Schulze distinguishes as granular 
collenchyma. From it to the sarcenchyma characteristic of sponges with aphodal 
chambers is but a short step. The granules of the granular collenchyma then evidently 
form a part of the collencytes, which have lost their stellate branching form and become 
polygonal by apposition. The gelatinous base of the original collenchyma is now reduced 
to a minimum, and the granular cells, now termed sarcencytes, lie so close together that 
usually no line of demarcation is visible. Occasionally, however, a narrow clear 
interspace can be discerned, and the composition of the sarcenchyma as a congeries 
of sarcencytes is thus made clear. The collenchymatous base probably persists, and 
we may regard it as a continuous medium in which all the cells composing the sponge 
are more or less immersed. 
Cystenchyme. — In some sponges, Pachymatisma and many others, including many 
Lithistids (PI. XXVII. fig. 14 ; PI. XXXIV, fig. 12), the collenchyma undergoes a 
modification of another kind, and this chiefly in the ectosome or its neighbourhood. 
The collencytes are replaced by or transformed into oval vesicular cells, with a thin 
but definite cell- wall, enclosing a small quantity of pale not deeply staining protoplasm, 
which lines the cell-wall as a thin layer, and extends in narrow threads to the protoplasm 
in which the excentrically situated nucleus is immersed. The rest of the cell is vacuolar. 
These vacuolar or vesiculate cells may lie in a collenchymatous matrix isolated from each 
other, or they may be so numerous and closely approximated that all trace of intervening 
collenchyma disappears. This vesicular connective tissue (cystenchyme), as has been 
already remarked by several investigators, naturally recalls the similar tissue in Mollusks 
and other Invertebrates. From a similar tissue may arise that which for want of a better 
name I have called cavernous collenchyma ; good examples of this occur in the Tetillidm, 
e.g., in Tetilla grandis (Pi. V. fig. 5). In this tissue the cell-walls of the vacuolate 
cells, which are accumulated in nests, appear to have broken down or fused together, and 
numerous large cavities result, each when first formed containing the protoplasmic remains 
of several cystencytes, but subsequently these appear to become absorbed and the cavities 
are left empty. 
Chondrenchyme. — In yet other cases the gelatinous basis of the original collenchyma 
acquires additional consistency, and some of the collencytes are replaced by round or 
oval granular cells, a tissue resulting, which bears a remarkable resemblance to hyaline 
cartilage {Throiribus challengeri, PI. VIII. figs. 35-37). Apparently no experiments 
have been made with a view to ascertaining whether this is chondrin-yielding or not. 
Thesocytes. — No tissue that can be called thesenchyme has yet been observed in any 
sponge, but in many cases, notably in Thenea, more or fewer of the collencytes are 
modified to form what may fairly be regarded as reserve cells or thesocytes. In an 
