192 SPONGES. 



produced by the sponge itself, and therefore not foreign; hence might be 

 termed " proper." 



Ord. V., Echinonemata.— Here we have only to add to the foregoing 

 an external set of proper spicules, which project vertically from the 

 surface of the fibre, like prickles on a hedgehog's back. 



Ord. VI., Holorhaphidota. — We lose the horny element here, 

 and, for the most part, the fibre is made up of proper spicules, held 

 together by the slightest quantity of sarcode ; or they may be dispersed 

 throughout an areolated sarcode, which, in the dried state, looks like 

 crum of bread. 



Ord. VII., Hexactinellida. — Again we have fibre here without the 

 horny element, but the fibre is vitreous, so that it is like spun-glass, 

 while all the spicules, of whatever form they may be, axiate its interior. 

 The spicules, too, are all developed upon a hexradiate type, (hence the 

 name of the order,) that is, the central point of the canal, (which 

 traverses all siliceous spicules, and upon whose extension in different 

 directions their ultimate forms respectively depend,) presents six buds or 

 lines radiating from each other at equal angles, so that, if surrounded by 

 a glass cube, they would meet the centre of each side respectively ; or 

 there may be no fibre at all, and the areolated sarcode when dry, like 

 " crum of bread," as in many of the Holorhaphidota, where the spicules 

 also are dispersed throughout the mass without any apparent 

 regularity. 



Ord. VIII., Calcarea. — -Here all the spicules, instead of being 

 siliceous, are, rninerally, composed of carbonate of lime. 



Of course these orders may be further divided into families, groups, 

 and species, for which I must refer the reader to my " Notes Introductory 

 to the Study and Classification of the Spongida," published in the 

 "Annals" and " Magazine of Natural History" in 1875, (Vol. XVI., pp. 1, 

 &c.) But it must not be assumed that there is any such classification in 

 nature, for this is only human invention to aid the human memory. 



Having now given an arrangement of the Spongida in which, 

 beginning with the simplest form, viz., the Carnosa, where there is no 

 permanent skeletal structure, we passed on to the Ceratina, &o., in which 

 there is one ; it may be further observed that this is also the course 

 followed by the development of the embryo of all sponges, so that before 

 the horny skeleton is produced, it is in the state of the Carnosa, where it 

 remains, if belonging to this order ; while in the sponges with horny 

 skeleton, it goes on till the latter is produced, before the development is 

 complete. 



To facilitate the comprehension of what a sponge is when minutely 

 examined, it might be stated by way of homely simile, that, in structure, 

 it is like a bunch of grapes which has been put into melted wax and kept 

 there until the latter is cool ; after which, being held up by the stem, the 

 wax still filling the interstices between the grapes, it is to be pared off 

 down to the level of the bunch and the whole put into a muslin bag 

 which is to be tied round the neck of the stem. 



