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THE VOYAGE OF H.M.S. CHALLENGER. 
subcortical crypts. These are surrounded by collenchyma containing numerous fusiform 
cells, which are collected in places into fibrous strands or felts. 
The walls of the larger canals in the choanosome are similarly constituted. The velar 
diaphragms of these canals consist of a middle layer of fusiform cells, faced on each side 
by epithelium, on the inner face of which chiasters are abundantly scattered. The fibrous 
tracts extending from the cortex along the sides of the spicular bundles are strongly 
developed. The flagellated chambers are small, about 0'022 by 0'02 mm. in breadth and 
length, they communicate by long aphodal canals with the excurrent canals, and with 
the incurrent canals by prosopyles (PI. XX. fig. 8). 
The chones have the irregular form usual in the genus (PI. XX. fig. 7). 
The bands for attachment are smooth, tough processes of the cortex, often attaining a 
length of 5 mm. or more. The attachment to a foreign body is brought about simply by 
an accurate adaptation of the two surfaces, that of the foreign body and that of the end of 
the process, to each other. A. longitudinal section of an average-sized band is shown 
in PI. XX. fig. 10. A narrow longitudinal fissure in the interior, continuing the direction 
of an irregular cleft at the attached end and lined by epithelium, remains to indicate the 
origin of the process in two outgrowths of the cortex, that have subsequently coalesced. 
A curved fissure, as shown in the figure, separates a more solid lower part from a cavernous 
upper part. The latter consists chiefly of coUenchyma excavated by numerous irregular 
cavities, and containing numerous vesicular and fusiform cells. The lower part is almost 
entirely composed of fusiform cells, lying in a stained matrix and running longitudinally 
downwards ; in fig. 11, which is turned sideways up, these are shown much folded by the 
contraction of the surrounding tissue. Between the fusiform cells oval unstained granule- 
cells occur, singly and in strings of two or three or more (fig. 9). Associated with these 
granule-cells are others of similar size, consisting of darkly-stained protoplasm, enclosing 
two or three vacuoles and a nucleus ; these appear to be the parents of the granule-ceUs ; 
other granule-cells in a state of exhaustion are present. The attached surface of the 
process is invested with epithelium, against which the fusiform cells terminate in the 
manner shown in fig. 12. 
The margins of the longitudinal fissure are represented as transversely striated in 
fig. 10. This is the appearance they present under slight magnification, more powerful 
objectives resolve this striation into a layer of small fusiform cells. At one end 
of the fissure these are continued into the general fibrous structure of the band, but 
elsewhere they are more or less separated from the main mass of fibres by the stained 
matrix of the fibrous tissue, free from fibres, but containing two or three dark irregular 
blotches, which have somewhat the form of multipolar ganglion cells. The fusiform 
cells are darkly stained and about 0‘04 mm. long, and the amoeboid cells, which look like 
blotches, occur near their inner ends. In any other position one might, but for their 
excessive numbers, suspect these fusiform cells of a sensitive function. 
