ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 233 



In a younger stage the gelatinous ring was found to be wanting ; in 

 its place tliere was a large cell which appears to be quite identical with 

 an endodermal cell, as it has a plasmatic plexus, and a large network ; 

 as to the fate of this cell nothing is yet known. This younger form 

 had only a single row of large endodermal cells, and these form a 

 circular lining to the gastric cavity ; each of the large cells assimilates 

 the neighbouring small cells. The resemblance between Cunoctantha 

 and Gastrodes is unmistakable; the endodermal dimorphism of 

 Gastrodes differs only from that of Cunoctantha in that the small cells of 

 the latter are at first completely covered by the giant cells. Morpho- 

 logical differentiation is more markedly exhibited in Gastrodes than in 

 Cunoctantha ; instead of one large cell there is a complete generation of 

 such cells, which have, however, lost their power of movement (formation 

 of pseudopodia) and only function as gastric digestive cells. 



Porifera. 



Stelospong^us flabelliformis.* — Mr. A. Dendy gives an account of the 

 anatomy and histology of this South Australian sponge, the characteristics 

 of which were briefly diagnosed by Mr. H. J. Carter in 1885. A specimen 

 was fortunately found containing a large number of enormous spherical 

 embryos, each as large as a small pea. The entire surface of the sponge 

 is thickly incrusted with sand-particles, which give a very hard, im- 

 penetrable character to the sponge, and must form an admirable protec- 

 tion against the attacks of the numerous parasites to which sponges are 

 very subject, and it functionally replaces the special dermal skeleton of 

 spicules which is found in very many siliceous sponges. 



The skeleton is thoroughly typical in structure and arrangement, 

 and is essentially the same as that of the bath-sponge, only much 

 coarser. A reticulate skeleton may be regarded as derived from the 

 radiate by a development of secondary fibres connecting the primaries ; 

 the majority, at any rate, of the so-called horny sponges are descended, 

 probably along several lines, from the Haiichondrina, by the gradual loss 

 of the spicules and the greater development of spongin in a reticulate 

 skeleton. In the species under discussion the skeleton fibres may some- 

 times be seen projecting freely from the surface of the sponge ; this'^s a 

 character often observed in siliceous forms. 



The canal system, which is carefully described, is seen to differ 

 little from the ordinary lacunar type so characteristic of the Haiichon- 

 drina. The outermost portion of the ectosome is formed by an extremely 

 thin and delicate epidermis ; cystenchyme cells are present, and the 

 stellate mesodermal cells appear to be thoroughly typical. The struc- 

 ture of the choanosome is considered under the heads of (1) the walls of 

 the inhalant and exhalant canals, (2) the walls of the embryo-containing 

 cavities, (3) the walls of the flagellated chambers, (4) the general mass 

 of mesoderm in which the chambers and canals are imbedded, and (5) the 

 spongoblasts and other mesodermal cells surrounding the skeleton 

 fibres. 



The ovum of S. flabelliformis lies in a fibrous capsule, and has a 

 longer diameter of 0*076 mm., while that of the nucleus, which lies at 

 one pole, is • 024 mm. All the embryos, except one or two of the 

 smaller ones, w^ere solid. The surface, under a pocket-lens, exhibits a 



* Quart. Journ. Micr. Sci., xxix. (1888) pp. 325-58 (4 pis.)- 

 1889. R 



