SPONGES. 57 



Of course these orders niii}' be further divided into families, t^roups, 

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

 to the Study and Chissilieation of the Spongida," [uihlished in the 

 "Annals'" and " ]V[aj,'azine of Natural History" in 187-'), (Vol. XVI., pp. 1, 

 d'c.) But it must not be assumed that there is any such chissilieation in 

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



Having now given an arrangement of the Kpt)ngida in which, 

 beginning with the simplest form, viz., the Cauxosa, where there is lui 

 permanent skeletal structure, we passed on to the Ceisatina, itc, in which 

 there i.i 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 Caknosa, 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 aud 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. 



In this condition the grapes resemble the spheres which contain the 

 animal parts of the sponge ; the wax in their interstices, the parenchyma ; 

 the holes between the fibres of the muslin, the pores or inhalent orifices ; 

 the stem audits branches, the excretory or exhalent canal system; aud 

 when there is a horny skeleton, &c., pi'oduced, as in the Officinal Sponges 

 this is developed in the midst of the parenchyma. 



Examining these parts more particularly, the individual sphere is 

 found to be lined with or composed of monociliated, monad-like infusoria 

 in juxta-position whose cilia wave into the hollow interior ; presenting 

 two or more openings in its wall which are respectively, in continuation 

 with tuVjular canals coming irom the pores on one side, aud going to the 

 excretorj' canal-system on the other, the former for bringing in the food 

 aud the latter for carrying off the refuse. Finally, the parenchyma serves 

 for producing the horny skeleton, &g., (where there is one,) aud the 

 temporary location of the reproductive elements, viz., the eggs aud the 

 spermatozoa, where, after impregnation, the former become ciliated all 

 over as they pass into the embryonal state, aud thus fitted for inde- 

 pendent existence, are discharged through the excretory canal 

 system. 



Subsequentlj', the embryo seeks some hard object for fixation and 

 further development, whei'e it remains growing upwards or horizontally^ 

 until it arrives at the form assumed by the matured species ; or, if by 

 accident or otherwise it becomes detached and free, then, by growing 

 equally on all bides at once, it may beconae globular. 



