120 AET. 7. 1. TJIMA I HEXACTINELLIDA, IT. 



sent species incloses nuicli \Yider meslies, which fact imparts a 

 more deUcate appearance to the entire ectosome. 



The hypodermal strands on the connh are seen to converge 

 towards the apex. The extreme apex is generally compact-look- 

 ing, owing to the crowded presence there of the dermalia. The 

 same may be said of the dermal surface at, or close to, the oscu- 

 lar margin. 



TJie subdermal space in the greater part of the sponge is 

 moderately wide. Strands of spicules j^ass up across it, at fre- 

 quent intervals, from the exceedingly uneven choanosomal surface 

 to join the hypodermal framework. 



Through the thin ectosome arc plainly visible the numerous 

 incurrent canalar apertures, 3 mm. and under in diameter. 



A thin and delicate endosomal layer lines the entire gastral 

 surface. The gastralia form a continuous lacework with quad- 

 rate meshes which are considerably larger than those of the 

 dermal Inyer. The layer appears as if sprinkled with white 

 powder, owing to accumulations of microsclerre. To the naked 

 eye, the presence of hyj)0gastral strands is in most places not 

 apparent ; but where the gastralia are sparse and scattered or 

 when seen under the microscope on preparations of the endosome, 

 the hypogastralia appear to form a thin-l:)eamed and compara- 

 tively wide-meshed latticework similar to the hypodermal. In 

 Acanthascus cactus the hypogastral l)eams (see PI. XL, fig. 16) 

 are somewhat coarser and inclose smaller meshes which moreover 

 open free instead of being covered over by a continuous gastral 

 lacework. Here then is another point which might serve in dis- 

 tinguishing between that and the present s^^ecies. 



The excurrent cannlar apertures are all small in the upper 

 part of the gastral cavity. Lower down, larger ones add them- 



