98 Mr. H. J. Carter on the Nature of the 



the water from the spherical cell, they will also there, in their 

 isolated state, become monociliated and unciliated polymorphic 

 organisms respectively. 



Lastly, if the young Spongilla which grows out from the hili- 

 form opening of the seed-like body be fed with carmine or indigo, 

 these monad-like organisms will be still more evidently seen 

 aggregated, in the midst of the intercellular substance, into the 

 form which I have called the " ampullaceous sac." I have 

 also lately termed the monad-like organisms " spongozoa," as 

 their peculiar form &c. seem to demand this distinction. 



Let us now consider what the " ampullaceous sac " is. 



In 1827, Prof. R. E. Grant (my kind friend and former 

 teacher), with exceeding truthfulness and great ability, described 

 the " ova " of the marine siliceous sponges (Edinb. Phil. Journ. 

 vol. xiii. & Edinb. New Phil. Journ. vol. ii.) as ovoid bodies 

 covered with cilia, which, after issuing from the sponge, sought 

 a place to settle down upon and become developed into a 

 miniature form of the parent. 



In 1856, Lieberkiihn discovered and figured the same kind 

 of body in Spongilla, to which he applied the name of 

 " Schwiirmspore " (Midler's Archiv f. Anat., Phys. &c. Heft 

 iv. pi. xv. figs. 35-39). 



In 1872, Hackel did this also, with his usual ability, in the 

 Calcisponges (' Die Kalkschwamme,' 1873, Text & Atlas) — 

 proposing the terms " Planula or Flimmerlarve " for the 

 advanced state of the ovum, and " Gastrula " for that of the 

 following embryonal form — that is, where the internal cavity 

 is formed but does not communicate with the exterior, and 

 where it does, respectively. 



Moreover Hackel, in several places, rightly figures the 

 Gastrula as consisting of an ectoderm or crust of monociliated 

 cells, radiating round the endoderm, which again is a layer of 

 much larger and unciliated cells lining the internal cavity in 

 juxtaposition (but not in radiation), and extending out over 

 the aperture of the Gastrula in a botryoidal form ; thus the 

 convexities of the latter are of course much larger than those 

 of the mulberry surface formed on the exterior by the ends of 

 the monociliated cells of the ectoderm. Hackel's illustrations 

 can hardly be too highly praised. 



Searching after these ova lately in the marine sponges, I 

 have as yet, from the examination of several gatherings, only 

 found them, in the stages of development just mentioned, in 

 Grantia compressa (Sycandra compressa, H.) ; that is to say, 

 the rest of the sponges have either passed through this ovi- 

 parous state, are coming to it, or, if in it here and there now, the 

 specimens I have obtained (which have been very numerous) 



