SPONGES PROM THE MEEGTJI ARCHIPELAGO. 



63 



Order I. CAENOSA. 

 None. 



Order II. CEBATINA. 

 None. 



Order III. PSAMMONEMATA. 

 Among the Psammonemata there is a small specimen of Spongia 

 officinalis ; three specimens of Polytherses with coarse, one with fine 

 or compact structure, and one incrusting a mass of bivalves ; three 

 specimens of Cacospongia, and nine of Dysidea. 



Spoxgia officinalis. 



Of the single specimen of Spongia officinalis there is nothing 

 to say beyond that it is genuine although small, not being more 

 than an inch in its longest diameter. 



Hiecinia, sp. 



The three large specimens of PolytJierses with "coarse" 

 structure are massive and sessile, with broad bases respectively, 

 ending superficially in short pyramidal processes. The latter 

 present the usual white lace-like reticulation over the poly- 

 gonal interstices which is common (although not always pro- 

 duced) in these sponges, and arises from an accumulation of 

 foreign bodies (fragments of the spicules of other sponges, sand- 

 grains, and the hard parts of many other microscopic organisms) 

 over the soft reticulated fibre which pervades the dermal sarcode 

 and gives support to the pores or inhalant orifices which are 

 situated in its interstices. This is the structure of a true Hircinia 

 before it has been transformed by the invasion of the terminally 

 swollen parasitic filament which I have described and illustrated 

 under the name of SpongiopJiaga communis (Ann. & Mag. Nat. 

 Hist. 1878, vol. ii. p. 168). It is to this transformation, which 

 is so much more frequently seen in almost all the Hircinice 

 than the original sponge itself, that has led many to consider it a 

 distinct genus, and among them Duchassaing and Michel otti, 

 who, in their account of the West-Indian Sponges (' Spongiaires 

 de la Mer Caraibe,' Haarlem, 1861).. first called it " PolytJierses.'''' 

 Many have endeavoured to unravel the nature of this filament, 

 but it still remains as enigmatical as ever. Still there can be no 

 doubt that specimens occasionally occur without the parasite. In 

 any case the external form of the sponge is generally sufficient for 



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