324 Mr. H. J. Carter on the 



examination subsequently made of the large pieces transported 

 to the pool, as above stated, far above low-water mark. Add 

 to this a basket and an old pair of boots to wade through the 

 water, which will be often much above the knees, and thus 

 protect the feet from being cut by the rocks and fragments of 

 shells adhering to them. 



Returning to the development of the sponge-ovule, I would 

 observe that the oviparous sponges gathered on the 30th July 

 have furnished me with all the observations needed for this 

 communication, and therefore that those gathered on the 29th 

 August were chiefly to corroborate the fact that about this 

 time the marine siliceous sponges will be found available for 

 the study. 



Again, I have not been able to follow up the development 

 of the ovule from its earliest appearance to that of the embryo 

 and fully formed sponge in any one species only, from circum- 

 stances which will hereafter be mentioned ; hence my illustra- 

 tions of the early stages have been taken from one, and those 

 of the later ones from another species. 



Most of these illustrations, too, have been drawn to the 

 same scale, viz. l-12th to 1-1 800th inch, in order that the 

 relative size of the different objects at different periods of 

 development may be the better realized. Thus, with the 

 exception of fig. 1 in Plate XX., all the figures, from 2 to 

 12 inclusively, which are taken from Halisarca lobularis, 

 are drawn to the scale mentioned ; so are the remainder of 

 the figures in this Plate (with the exception of the slight de- 

 tail otherwise noticed), which have all been taken from Grantia 

 coinpressa, in order, as before stated, that their sizes, rela- 

 tively and respectively, may be compared with the figures of 

 the embryos of Halisarca lobularis in the same, and of Hali- 

 chondria simulans in the following Plate, in which the figures 

 appear to be unusually large, but, to still preserve the scale 

 for the purpose above mentioned, it was necessary that they 

 should not be reduced ; while in the third Plate, on account 

 of the increasing size of the embryo after it begins to pass into 

 the true sponge, and for other reasons which will be noticed 

 hereafter, the figures, for convenience, have been reduced to 

 the scale of l-12th to l-830th inch : thus it should be re- 

 membered that, for comparison with the foregoing, they should 

 be more than double their present size. 



By the illustrations in Plates XX. and XXI., having been 

 drawn to the same scale, we are able to realize the relative 

 sizes of the embryo of the gelatinous sponge, or Halisarca 

 hbularis, of the calcareous sponge, Grantia comprcssa, and 

 of the siliceous one, Halichondria simulans, respectively. 



