218 ARTHUR DENDY. 



be very conspicuous in sections taken at right angles to its 

 surface. 



In an undetermined specimen of Leucandra, from Port 

 Jackson, the epithelial cells lining the gastral cavity just within 

 the osculum are so much swollen out as to be almost as thick 

 as they are broad, and they also present a vacuolated blister- 

 like appearance, as shown in fig. 33. Lower down in the gastral 

 cavity the epithelial cells have the normal flattened form. 



The flagellated chambers of most, if not all Heterocoele 

 sponges, whether they be of the elongated Syconoid or of the 

 rounded Leuconoid form, are separated from the exhalant 

 canals into which they open by very distinct membranous 

 diaphragms (figs. 25 — 27, 31). When viewed en face these 

 diaphragms have usually the appearance shown in fig. 31, 

 consisting of a thin, transparent membrane, in which are 

 visible spindle-shaped cells arranged concentrically. The 

 actual outlines of the cells I have not succeeded in distinguish- 

 ing, but their elongated character and concentric disposition 

 are usually clearly indicated by the arrangement of the 

 granules which surround the nucleus. Collared cells are never 

 found on either surface of this membranous sphincter, and 

 whether it consists of one or two layers of cells is a very 

 difficult question, which I have not been able definitely to 

 decide. The concentrically arranged, spindle-shaped cells 

 are obviously muscular, and as such I described them in my 

 memoir on Grantia labyrinthica. In that paper, however, 

 I classed them as mesodermal elements. I am now convinced 

 that they are simply modifications of the cells which line the 

 exhalant canals, comparable to the muscular cells of the oscular 

 diaphragm described by Minchin in Leucosoleuia, and by 

 myself in Vosmaeropsis. Fig. 27 shows how the epithelial 

 cells of the exhalant canal are continued on to the surface of 

 the chamber diaphragm. Usually they appear very much 

 elongated in this situation, as shown in fig. 31, but sometimes 

 the elongation is scarcely visible at all, as shown in figs. 25 

 and 26. Probably the exact form of the cells depends upon 

 their state of contraction. The epithelial cells of the exhalant 



