ASTROSOLERA WILLEYANA, THE TYPE OF A NEW FAMILY OF SPONGES. 469 



The soft tissues of the interior of the sponge are contained in the skeletal canals 

 and penetrated by the water-bearing canals which open by the pores at the surface. 

 From the main canals small ones are given oft" which ramify in the layer of soft tissue 

 in contact with the skeleton. 



As the canals are followed downwards into the interior, the cellular elements in 

 their walls, at first scattered, become more and more abundant, and the jelly less 

 conspicuous. In some parts of this intermediate region large coarsely granular cells 

 are abundant in the jelly. At a short distance from the surface the soft tissue 

 assumes the characters which are maintained throughout the interior (Fig. 12). 



The appearance of a section through it (Figs. 14 and 15 — 17) suggests that it 

 is largely made up of cells united into a reticulum, with vacuolar spaces of various 

 sizes forming the meshes. The jelly, which is so conspicuous in the surface layers, 

 appears to be scanty or altogether absent here. Besides the smaller, branched proto- 

 plasmic masses, with small nuclei (1".5 — 2fi in diameter) which make up the greater 

 part of the reticulum, there are larger and more circumscribed cells with larger nuclei 

 (2 — 3/x). Scattered through the reticulum, and with their walls apparently formed by 

 portions of it, are ciliated chambers and the ramifying branches of the canal sj-stem. 



Ciliated chambers (Figs. 15 — 17). The.se are round or oval chambers of minute 

 but fairly uniform size, the larger measuring 18 by llfi, the smaller 10 by 8/i. (The 

 sections of smaller diameter are doubtless, in many cases, transverse to the long axis of 

 larger chambers.) Their walls appear to be formed by cells which send out processes 

 laterally, and these, joining with one another, bound the chamber; other processes 

 extending away from the chamber are continuous with other cells of the reticulum, 

 while a thii'd set of processes project into the cavity of the chamber, and each, 

 tapering gradually from its base, forms a flagellum which may extend across to the 

 other side of the chamber. There is no indication of a collar or of the abrupt truncated 

 termination of the cell-body at the base of the flagellum, which are usually seen in 

 choanocytes. A well-marked nucleus is situated at the base of the flagellar process, at 

 its junction with the body of the cell. The flagella project from about half the inner 

 surface of the chamber, some four or five commonly appearing in section, and their 

 tips thus converge and are often seen to have become entangled. The remainder of 

 the inner wall of the chamber is smooth and at some point in it the cavity opens 

 into a branch of the canal system by a narrow passage, about 4/i in diameter (Fig. 17). 

 This is only rarely seen as a distinct passage, owing to its narrow lumen. 



Considering how readily the collar cells of sponges lose their characters unless 

 special measures are taken to preserve them, it cannot be assumed that the condition 

 above described of the cells lining the ciliated chambers is precisely that of the 

 living state. It is perhaps possible that they had in life the usual characters of 

 collar cells, but if so. it is curious that while the flagella are preserved they should have 

 lost not only their collars, but also the truncated shape of the ends turned towards 

 the centre of the chamber. And, in view of the unique character of the skeleton of 

 Astrosclera it is quite possible that the cells of its ciliated chambers were also of a 

 peculiar type. We cannot, with the present material, arrive at certainty on the pouit. 



w. IV. 63 



