Sponges from South Australia. 433 



The calcareous sponges were divided by Hackel into three 

 families, viz. " Ascones, Leucones, and Sycones," which, 

 for very satisfactory reasons, Dr. Pol(ijaeff (Report, p. 22) 

 has reduced to two divisions, viz. " Homocoela and Hete- 

 rocoela," the former including the single family of Asconidaj 

 (Ascones), and the latter those of the families Syconid^ (Sy- 

 cones), Leuconidge (Leucones), and Teichonidee (Teichone, 

 Teichonellidffi), — the chief differences between the two being 

 that in the division Ascones or Homocoela there is apparently 

 no parenchymatous tissue, that is, the sponge is almost 

 entirely reduced in structure to a mere tube whose wall hardly 

 amounts to more than a thin layer of spicules held together 

 by and supporting the sarcode (syncytium, H. in part) which 

 contains the soft portions of the species, but branching, anas- 

 tomosing, and rebranching continually during growth, at 

 length may reach a more definite form ; while in the Hete- 

 rocoela the tissue supporting the soft parts fills up as it were 

 the spaces between the bends of the tortuous tubulation in the 

 Ascones, and thus produces a massive sponge like Tei'cho- 

 nella proliferaj which in structure closely approaches an 

 ordinary non-calcareous sponge. I have said " as it were," 

 because the " tubulation " does not exactly represent the 

 excretory canal-system of Teichonella proJifera^ which is den- 

 driform, while that of a tubular Ascon is more or less of the 

 same calibre throughout. However, this broad distinction 

 will do for the present, as I shall have to return to the subject 

 more particularly hereafter. 



But in so far as many of the Sycones are as much reduced 

 to a simple tube in their structure as many Ascones, so P shall 

 transpose Hiickel's primary or family divisions as Dr, Pol^jaeff 

 has done, by placing the Sycones before the Leucones and 

 the Teichonellidaj last ; thus we shall have an uuinterrupted 

 evolution in structure from the simple tube in the Ascones to 

 the most complicated form of that in the Teichonellida^, or, at 

 least, T. j)rolife.ra^ for we shall find by-and-by that it will be 

 necessary to place T. lahyrinthica among the Sycones, as its 

 structure is almost precisely that of Grantia compressa. 



Meanwhile it is necessary to begin by defining what a 

 calcareous sponge is, and this may be done by stating that it 

 is a spiculiferous sponge in which all the spicules are cal- 

 careous. 



After which it may be added that it possesses no fibre, 

 which, together with its tender structure generally and 

 the delicate structure of the excretory canals, rend'ers its tissue 

 more or less fragile in every instance. 



