PORIFERA. 795 



wide, the ampullae have many inhalent pores ; when fine and tubular, 

 several tubes may open into the same ampulla. This fourth type is found 

 among Calcarea Heterocoela in the Leuconidae, and so far as is known 

 also in the Teichonidae and in all thoroughly investigated Non-Calcarea 

 except those under (3) supra' 1 . The inhalent and exhalent canal systems 

 are branched and of considerable extent. The superficial pores may lead 

 either directly into ampullae or into canals which branch only slightly, 

 e. g. Oscarella lobularis ; into canals which first unite and then branch, 

 e.g. Chondrosidae ; through pore-membranes either directly or indirectly 

 by a narrow canal into a more or less extensive system of subdermal 

 spaces, from which branching canals take origin a very general mode. 

 In the Geodidae and several Ancorinidae the pores may open each into 

 a cortical funnel (hops), or into narrow canals which unite, or into sub- 

 dermal spaces, from which in either case cortical funnels lead into a system 

 of anastomosing subcortical crypts, and these in their turn into the inhalent 

 canals. The exhalent canals may be wide spaces, or slender canals, uniting 

 together to form larger and larger spaces or canals, which open finally 

 into an oscular tube. The length of the latter varies ; when very short 

 it is often termed cloaca. Isops has exhalent cortical funnels comparable 

 in all respects to the inhalent 2 . 



The subdermal spaces and subcortical crypts are not to be con- 

 founded. The former lie immediately beneath the outer surface, covered 

 by a thin layer of sponge substance : they are large simple cavities 

 usually communicating one with another 3 . The subcortical crypts form 

 a set of anastomosing cavities between the cortex and medulla, i. e. at 

 a deeper level than the subdermal spaces. The funnels or chonae (supra} 

 are divided by a constriction into an outer part, the ectochone, long and 

 cylindrical, and an inner part, the endochone, short and more or less 

 hemispherical 4 . Other structures to be noted are the endogastric septa 

 of Haeckel, cords or membranes extending into or across the oscular tube 

 and anastomosing together. They are of secondary origin and occur in 

 both divisions of Porifera 5 . 



1 Polejaeff states that pore-canals to the ampullae are wanting sometimes in Spongidae ; Kera- 

 tosa, op. cit. p. 1 7. Transitional or variable forms between types (3) and (4) are certain to occur, 

 and probably not infrequently. 



2 In the Auleninae, the sponge appears to have a very irregular mode of growth into processes 

 or lamellae. The intervals between the lamellae, &c., are generally traversed or protected by per- 

 forated membranes, thus becoming lacuniform. The lacunae are common both to the pores and 

 oscula. Von Lendenfeld, Proc. Lin. Soc. New South Wales, x. p. 283 ; cf. his table, p. 490. 



3 The spaces in question are traversed in Bajalus by anastomosing filaments, in Dendrilla by 

 slender vertical filaments, in both cases composed of mesoglaea covered by epithelium. 



* For the subcortical crypts and funnels, see Sollas, A. N. H. (5), v. pp. 135, 140, 252 ; and on 

 Isops, pp. 396, 402. 



5 See Haeckel, Kalkschwamme, i. p. 252 ; Vosmaer, Mitth. Zool. Stat. Naples, v. p. 489, and 

 Porifera, Bronn's Thierreich, &c., ii. p. 128. 



