a7id Functions of the Sponge. lil 



of the S. panicea, and a specimen of moderate size may be com- 

 puted to discharge at least ten thousand ova every season. The 

 smaller species are much more prolific. On cutting an ovum 

 transversely through the middle, the ciliae on its anterior half con- 

 tinued in motion for twenty-four hours. On tearing an ovum to 

 pieces with two needles on a plate of glass, we perceive, by the 

 aid of the microscope, about twenty rudimentary spicula occupy- 

 ing its central opaque part, and having the same form with those 

 of the parent. The ovum does not show any power of changing 

 its form, during its most active state, which the ova of some high- 

 er zoophytes distinctly exhibit. During the months above men- 

 tioned, every specimen of the panicea is found crowded with ova ; 

 some presenting them in a more advanced state than others, and 

 the same specimen presents them in every stage of maturity. 



In about two or three days after the ova of the ^S*. paiiicea 

 have separated from the body of the parent, we observe them 

 beginning to fix themselves on the sides and bottom of the ves- 

 sel, and some of them are found spread out like a thin circular 

 membrane on the surface of the water. Those which have fixed 

 on the sides of the vessel, have a more regular circular outline 

 than those on the surface of the water, which have often a torn 

 appearance, with holes of difi'erent sizes through them ; but in 

 all those which have thus fixed and spread out like a thin trans- 

 parent film, we can very distinctly perceive, with a single lens, nu- 

 merous spicula, disposed without any apparent order throughout 

 their central parts. On immersing several watch-glasses in a ba- 

 sin of sea-water, containing many specimens of the S. panicea in 

 the act of discharging their ova, I found, after a few days, that 

 most of the ova had fixed on the outside of the watch-glasses, so 

 as to have their pores and orifices, when fully grown, vertically 

 downwards, and almost none were in the concavities of the watch- 

 glasses, where I wished to collect them. It is easy, however, to 

 cause them to fix and grow in the concavities of watch-glasses, 

 by placing them there near the natural time of their fixing, when 

 the ova exhibit much less inclination to swim about ; and the 

 progress of their development is most conveniently watched when 

 they are caused to grow in that situation. When we examine 

 the ova through the microscope, while in the act of fixing on the 

 surface of the glass, we find that they are always so placed^ 



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