Elements of the Spongida. 353 



it is evident that at this stage, viz. when the ampunaceons 

 sac and the ovum are seen together, the exact position of the 

 latter can be easily determined. 



If, then, it be assumed that each spongozoon is the animal 

 representative par excellence of the sponge (that is, that it 

 contains both alimentary and reproductive organs), then it may 

 be assumed that it possesses an ovary, and that the ovum 

 originally comes from this source. It does not follow that all 

 the ovicells of an ovary should be fertile or finally produce a 

 new being if any, or that the whole of the spongozoa of the 

 ampullaceous sac should, as in the present instance, be not 

 called into requisition to produce a single ovum ; for Nature is 

 by no means particular in these matters so long as she can 

 effect her object in a single instance, that is, the reproduction 

 even of a single being. 



With reference to the season during which the sponges in 

 this country produce and ripen their ova, I can only state 

 from actual observation that, in the Calcareous Sponge called 

 " Grantia compressa^'' this takes place between the months 

 of March and June inclusively. In March the ova begin to 

 appear, in April they are very evident, in May all three stages, 

 viz. ova, segmentary, and embryonal, may be present, in June 

 the embryonal form is abundant, and by the end of July they 

 have left the parent in an effete and apparently exhausted 

 state, after which I do not know what becomes of it. 



Thus, so far as Grantia comfrressa goes for this locality, I 

 think the student may safely depend on these data, while 

 during all this time a plentiful supply of the species may be 

 obtained from little pools in the rocks, which often exist 

 almost as high up as " high-water mark ;" therefore at any 

 time between high and low water they are easily accessible. 



I cannot say so much for the calcareous sponges in this 

 locality, as it was not my purpose to follow the development 

 of the ovum in them in the same way; but from having 

 found so many siliceous sponges in an ovigerous condition 

 about the month of August, I should say that this would be the 

 best time to look for them also, although hundreds of speci- 

 mens may be examined before meeting with one sponge that 

 is ovigerous. 



Then, for the student who wishes to follow the reproductive 

 process throughout, hoping perhaps that he may thus also 

 see the spermatozoa, it is not only necessary to find a speci- 

 men in an ovigerous condition, but to know when the ova 

 begin to appear and when they have passed into the embryo- 

 nal state ready for exit in the species which may have been 

 selected for observation. 



