, • . DlCTY08P0N<lIDiK. 



14 



the reticulate siliceous sponges, an opinion which all later investigations have 



tended to confinn* 



All that is now known with reference to this family of the silice- 

 ous sponges, the Dictyospongid^., has been brought together in this 

 volume The last ten years have vastly increased the number of known forms 

 and demonstrated that in certain late Devonian and early Carboniferous 

 faunas they were abundant in individuals, species and genera. The accounts 

 of the species previously described have been for the most part brief and 

 either insufficiently illustrated or entirely without illustration. In addi- 

 tion to the representation here given of the general aspect of these forms, 

 there is added, where the material permitted, a microscopic analysis of 

 the spicular skeleton. 



General Observations on the Sponges. 

 The Sponges, wth the exception of a few forms inhabiting fresh waters, 

 are marine animals, and among the lowest and simplest in the scale of 

 life. Less simple than the Protozoa, they are also of less complicated 

 anatomy than typical Coelenterata (anemones and corals), and there is an 

 inclination among some later investigators to recognize them as a distinct 

 sub-kingdom of the animal world. 



A7U,tomy. A sponge is an aggregation or colony of simple cells; a 

 mass of connective tissue lined without and within by obscurely differentiated 

 layers. Together, these usually form a sac-like body, attached at the lower 

 or closed end, and to its interior cavity (paraffaster) the water has free access 

 by means of canals, extending from the exterior surface and opening upon 

 the walls of the paragaster. The course of the water currents is, thus, 

 centripetal over the general surface of the sponge, and centrifugal from the 

 paragaster through the osculum or mouth of the sac. 



Among the cells of the outer epithelial layer which lines all the canals 

 leading into the internal cavity, are scattered numerous flagellate cells, by the 

 action^ of whose long " whip-lashes " the flow of nutrient water currents is 

 produced and determined. Such flagellate cells are aggregated in little 



• Previous to 1881 there ha.l boon only vague suggestions of the sponge-nature of these fossils. The 

 .low to their real character was first furnished by the introduction into the museum '"•»«';t'°"« "^ I'"" 

 country of the exquisite glass-sponge kno^vn as the "Venus flower-basket " and described by the late 

 Richard Owen as EnpUctella aspergiUum. Although this description dates as far back as 1841, he 

 species was a very great rar.ly in collections here until fifteen or twenty yearsago. About that t.me the 

 sponge fishers of the Philippine Islands, the seas of which are the favorite habitat of the spec.es, « nttcd 

 the market, so that in England, according to Sir Wyvillb Thomson, the price of good specimens tell at 

 once from five pounds to ten BbiUings or less ( rft« Atlantic, p. 136, 1878). 



