PORIFERA. III. 21 



anterior wall is higher than the posterior, which is towards the sponge, e. g. 6 and 3"' respectively. 

 The elliptical opening is covered by a somewhat immersed pore-membrane, with very close-lying pores, 

 so that the membrane is sieve-like; the pores have an average diameter of O'ly 111 " 1 . The walls of the 

 papillae are provided with spicules which do not lie in the longitudinal direction, as is also the case in the oscular 

 papillae; they are here distinctly arranged in two sets of bands crossing each other more or less rectangularly, 

 and placed more or less obliquely to the longitudinal axis of the papilla; this oblique direction shows 

 for the rest a definite arrangement; while the bands on the hinder side of the papilla form an angle 

 of 45 to the longitudinal axis, those on the anterior side are more erect and most so on the middle 

 of the anterior side; the bands form by their arrangement a close reticulation with square or subqua- 

 drangular meshes. In the pore-membrane no spicules are found. The oscula are present in greatest 

 number e. g. up to seven, of pore-papillae on the contrary only one or two are found. 1 ) The surface 

 of the inner body shows under the microscope an appearance almost as in Histoderma appendicTdatum ; 

 through the surface shine the openings of close-standing incurrent canals; the course of the water- 

 current will thus be through the pore-sieves into the extended subdermal spaces, from here through 

 the fine pores in the surface of the inner body into the canal system, and then out through the oscula. 



The skeleton. The skeleton of the dermal layer consists of tangential spicules in several layers; 

 the spicules are rather close-lying, but yet the tissue may everywhere be seen between them; they 

 intercross each other in all directions without any observable order, only a slight tendency towards 

 collecting into bundles is seen, with only few spicules in the bundles. The skeleton of the oscular and 

 pore-papillae is described above. The skeleton of the inner body. As in /. pdlicula a close examination 

 shows that the inner body also in the present species is provided with a skeleton; in the interior this 

 skeleton consists only of quite single scattered bundles, but on the other hand it forms distinct fibres 

 at the surface, running parallel with this, and it is thus in the main constmcted as in the species 

 of Histoderma. As far as I could observe no spongin is found in the skeleton. 



Spicula : a. Megasclera are of one form, strougyla, they are more or less, generally somewhat 

 irregularly curved, more rarely straight; sometimes the curve is somewhat sharp; they are thickest in 

 the middle and taper somewhat towards the ends but most frequently only to a slight degree. The 

 length varies a deal, from 0-66 no mm , they are rather slender, the thickness is in the middle cron 

 0-014 """ Fine developmental stages, which are monactinal, are found in the inner body. 



Embryos. In a couple of specimens embryos were found; they were lying in the inner body- 

 close to the dermal layer; they are globular, of a diameter of about 0-48 mm ; the examined embryos 

 showed no spicules. 



Whether this species is really identical with Topsent's viridis it is difficult to decide, but as 

 the only difference is, that the spicules in Topsent's species are somewhat smaller, 076""", there is 

 good reason to take them as identical. When Topsent declares, that the inner body is quite 



') Since this was written the work of Kirkpatrick (Nat. Antarct. Exp. Nat. Hist. IV, 1908) has appeared; here 

 the author describes a very interesting species I. Belli (Joycuxia) (41, PI. XVI, figs, i- 5 a); this beautiful Injtatella. has on the 

 surface numerous papillae, easily seen to be oscular and pore-papillae; the pore-papillae are about I cm long, trumpet-shaped, 

 with a pore-sieve over the wide opening; the oscular papillae are simple and smaller, about 4""" long. In this species the 

 facts with regard to oscula and pores are thus principally the same as described above, but both kinds of papillae are much 

 more developed. 



