294 ERYLUS ROTUNDUS. 



composed of polyedric parts. It is ]iossible that the sj^aces between these cells 

 and the walls of the cavities, within which they lie, and which appear to be emptj', 

 are in reality thick, hyaline, cell walls. Bnt a.'! these spaces are not stainable 

 with any of the stains (eosin, malachite-green, magenta, aniline-blue, methyl- 

 \i(ilct. azui'c, haematoxylin, aurantia, Bismarck-brown), I think this improlj- 

 ai)le. The cells composed of parts are much more numerous than the simple, 

 undixiiicd ones. The latter are scattered quite irregularly between the former 

 and do not iiuii'a.'^e in number either towards the surface or towards the interior. 

 Although convinced that the undivided ones and the ones composed of polyedric 

 ]jarts are merely different stages in the development of the same kind of cell, 

 I am unable to say whether the simple ones arise from the composed ones or 

 vice vei'sa. 



In the sections of var. typica, form B, groups of broad, irregularly oval cells, 

 ^ 28-32 fi long, were observed in the distal part of the choanosome. The plasm 

 of these cells is granular and each one contains a large nucleus, about 8 u in 

 iliameter. These cells appear to be ova. 



In the sections of var. ddaris A'oung larvae were obser^'ed. Some of these 

 laj' free on the canals, others appeared to be just on the point of emerging from 

 the cavities of the ground substance in wliich they were bred. These larvae 

 are spherical, measure 50-60 ju in diameter, and appear to consist of a central 

 granular mass, surrounded by a single layer of roundish, not elongate cells 

 about 8 a in diameter. 



In the choanosome of var. typka, foi-m D, large numbers of monocellular 

 s_vml)iotic .Vlgae were observed. These are spherical or oval, measure 15-20 /i in 

 maximum diameter, and have a stout cell wall about -4 /« thick. 



Canal-systc))). The uniporal entrances to the canal-system are usually 

 circular, and, when (juite open, 100^250 /i wide. Dilated pores of this width 

 are however not frequent, most of the pores being more or le.ss contracted and 

 smaller, or closed altogether. The flagellate chambers are more or less spherical 

 and measure 14 23 /« in iliameter. Those of var. cidaris are smaller (diameter 

 14 17 /() than those of the othei-s. The collar cells clothing them are not numer- 

 ous, distant, rather slender, and 4-6 /i long. The larger canals are surrounded bj'^ 

 stout mantles of tissue free from megascleres and flagellate chambers. Some of 

 them are traversed by sphincter-membranes. Such have been particularly 

 observed in vav. typica, form B. In the fonns C and 1) of var. typica and in var. 

 cidaris no apertures much larger than the pores described above, were observed 

 on the surface. In these sponges the efferent openings (oscules) do not seem 



