484 HYATT'S REVISION OF THE 



the young, which is always solid/ we may have either the fistular tube built up, or solid 

 branching forms, or combinations of both, the fistular arising from the solid and branching, 

 or, vice versa, the solid and branching springing from the sides of the fistular. Some of the 

 Aplysinte have a similar extensive range, but generally the variations ai'e more limited ; 

 whereas among the Sponginaj the filling out of the entire series indicated above, is the rule, 

 and any constancy the exception. Thus Sjiongia graminea, Dysidea frarjills and Hirclnia 

 purpurea, are exceptional, in so far as the species may be characterized to a certain extent 

 by their forms, but these species are the least known of the group, and this can only be 

 regarded, therefore, as a doubtful conclusion. It very often happens, also, that in a given 

 locality a certain series of forms may be shown to be peculiar to the species ; but these are 

 likely to be indefinitely modified by the discovery of new localities, or new situations in the 

 same locality. 



The microscopical composition of the little tufts of primary fibres varies so that I can make 

 no great use of them, as Schmidt claims to have done among the Mediterranean commercial 

 sponges of the genus Spongia ; but in the other genera the arrangement of the fibres in the 

 interior is much more characteristic, and gives excellent specific characteristics. The size and 

 fineness of the fibres and the mesh of the skeleton, are also of great value, but the most 

 reliable characteristics are obtained from the surface of the prepared skeletons among the 

 commercial sponges. Though still very important among the remaining genera of the sub- 

 order, the surface is more characteristic of the genus than of the species. This is due to 

 the fact that in Spongelia, Stelosj^ongos and Dysidea, the character of the surface is more 

 largely due to the nature and composition of primary or vertical fibres, which project more 

 or less, whereas in Spongia proper the surface is very often less eftected by the composition 

 and form of the projecting tufts of primary fibres than by those which I have called sec- 

 ondary tufts, which are simply irregular projections of the mass of the skeleton. 



This will be recognized by the study of the various forms of the American sub-species, 

 " tuhuUfera," which has a peculiar even surface, similar to that of the European Spongia 

 officinalis or cup-sponge, or by following through the various forms of Sjiongia equina, 

 sub-species gossyj^ina, with its extraordinarily tufted surft\ce, or Spongia agaricina, sub- 

 species corlosia, variety dura, with its hirsute exterior. In other genera no such wide 

 differences exist between the external aspect of the varieties or species, the diflerences being 

 principally in the greater or less fineness of the fibres and the mesh of the skeleton. 



The great difficulty which is experienced in any attempt to distinguish species results 

 from the extreme susceptibility of all keratose sponges to any change in external condi- 

 tions. They appear to require for the production of the forms in abundance, tropical or 

 sub-tropical seas, and attain by fiir their greatest development in the number of tlie forms 

 and species in the West Indian Seas. The typical forms, the commercial sponges, are essen- 

 tially confined to the waters of the Carribean Islands, Bahaman Archipelago, and the south- 

 ern and western coasts of Florida in this hemisphere, and to the Mediterranean and Eed 

 Seas in the other. Australia afibrds a few forms, and I have heard, though I cannot sub- 

 stantiate the fact, of some species on the Atlantic coast of Brazil. Bermuda also has a few 

 of the commercial kinds, which, according to Mr. Goode's report and the suite of specimens 



1 That is to Siiy, a bulb with but oue orifice or true cloacal oscule. 



