148 THE SPONGES. 



Plate 24). A small osculum, about 0.5 mm. in diameter, lies in the 

 centre of the area, and this is surrounded by a few other, usually smaller, 

 apertures, or by the ends of canals abutting against the dermal membrane 

 and appearing as apertures. The oscula lead into canals of corresponding 

 size which penetrate, radially or obliquely, deep into the body of tlie 

 sponge, where they continue to be surrounded with collenchyma as at 

 the surface. The mass of collenchyma surrounding the main efferent 

 canal, as may be seen in sections taken vertically to the surface of the 

 sponge (Figs. 3 and 4, Plate 24, sections passing entirely through the 

 lamellate body), passes through tlie body from one surface to the other, 

 and is honeycombed by numerous smaller canals. The main efferent canal 

 itself, on the other hand, which is well shown in tlie middle of the micro- 

 photograph. Fig. 3, Plate 24, does not appear to pass through the 

 entire thickness of the body. The collenchymatous tracts botli at the 

 surface (Fig. 2, Plate 24) and in the interior (Figs. 3 and 4, Plate 24) 

 lack the skeletal reticulum, which everywhere permeates the intervening 

 regions. 



The kind of structure, which has just been described, is obviously to be 

 regarded as a modification brought about by the excessive development 

 of collenchyma round the main efferent canals, coupled with the diminution 

 in diameter of these canals. The specimens exhibiting the reticulate 

 modification are elsewhere like the other individuals, the body being 

 penetrated by the common larger type of efferent canal, the surface 

 appearing uneven, uniformly dense, without obvious collenchyma, and 

 showing irregularly scattered oscula about 1 mm. in diameter. 



The pores, measuring 60-150 fx in diameter, are scattered irregularly 

 but thickly on both surfaces of the body over the solid tissue intervening 

 between the oscula, vestibular spaces, or the reticulately arranged collen- 

 chymatous areas. The flagellated chambers have a shrivelled appearance 

 due doubtless to the faulty preservation. They now measure about 20 /x 

 in diameter, and their arrangement indicates them to be eurypylous. 



Spicules. McgasclcrcB. 1. Style, 210-220 /x x 12-16 /x. Fig. 8, Plate 20. 

 Spicule nearly cylindrical, slightly curved, spinose with small sharp prickles. 

 The prickles are more abundant near the ends, less abundant in the middle. 

 The extreme point is smooth. Rounded end and spinose region near the 

 point sometimes slightly dilated. 



2. Tylote, 220-240 /x x 7-8 /., Fig. 9, Plate 20. Spicule slightly 



