THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 84. DECEMBER 1874. 



L. — Development of the Mariyie Sponges from the earliest 

 recognizable Appearance of the Ovum to the Perfected 

 Individual. By H. J. Carter, F.R.S. &c. 



[Concluded from p. 337.] 



Development of the Embryo of the Calcareous 

 Sponges. 



For this purpose I must confine myself entirely to Orantia 

 compressa, which, growing much above low-water mark and 

 chiefly on the branches of the little delicate seaweed Ptilota 

 sericea as it festoons the ledges of the overhanging rocks, exists 

 in a most convenient position for examination, inasmuch as, by 

 cutting off the branch of Ptilota, we can reduce the foreign 

 object on which the sponge grows to a very minute size 

 without interfering with the sponge itself ; added to which, 

 the bent club-shaped form of its surface-spicule (Plate XX. 

 fig. 20) is so peculiar that, even in the minutest forms, the 

 species can be determined by its presence. 



The walls of this little purse-shaped sponge are, in the 

 months of March, April, and May, charged witli the embryos 

 of the species, as well as ova, from their earliest recogni- 

 zable form up to the matured state of the embryo just before 

 its exit. Here I might observe that in the months of June 

 and July, after the embryos have been issuing from this 

 sponge for some time in great abundance, they may be found 

 fully developed and in groups of all sizes on the branches of 

 the Ptilota, immediately around the parent, where, although 



Ann. & Mag. N. Hist. Ser. 4. Vol. xiv. 28 



