SPONGES. 



193 



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 and its branches, the excretory or exhalent canal system; and 

 when there is a horny skeleton, &c, produced, as in the Officinal Sponge, 

 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 tubular canals coming from the pores on one side, and going to the 

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

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

 for producing the horny skeleton, &c, (whei-e there is one,) and the 

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

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

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

 pendent existence, are discharged through the excretory canal- 

 system. 



Subsequently, the embryo seeks some hard object for fixation and 

 further development, where 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 sides at once, it may become globular. 



The Officinal Sponges, which are divided into the finer and more 

 compact or " Turkish Sponges," which are the dearest, and the coarser 

 and less compact or " Honeycomb Sponges," which are the cheapest, 

 grow on the rocks throughout the Torrid and Temperate Zones under 

 more or less modified structure, but the most marketable hitherto found 

 come from the Levant and the neighbourhood of the Bahama Islands, in 

 the West Indies, respectively, where they are obtained by divers, who 

 cutting them off, bring them to the surface in baskets ; after which the 

 soft parts are diained away in the sun and the imperishable skeleton 

 having been finally cleansed is thus fitted for sale in the marketable parts 

 of the world. 



Sponges are so easily propagated by " cuttings," when properly treated 

 that this has been taken advantage of in the Adriatic for growing the 

 Officinal species. 



At present it is not determined where the Spongida should be placed 

 in the animal scale, although, of course, very low down, but when more 

 is known of their structure and species, those alliances will be found to 

 which I have before alluded, and their present enigmatical position thus 

 demonstrated. 



Of the important part that the Spongida have played in the geolo- 

 gical history of the earth there is no longer any doubt. Their remains 



