208 



GEODINELLA ROBUSTA. 



of the canals stout bands of longitudinal, spindle-shaped, finely granular ele- 

 ments, 3-5 ;t thick in the centre, are met with. Occasionally more or less iso- 

 lated, spindle-shaped elements, attaining a maximum transverse diameter of 

 10 /«, are seen in the sections. I have often noticed that the substance composing 

 these elements differs from the surrounding tissue, not only by being less stain- 

 able, but also by having a higher refractive index, so that it to a certain extent 

 resembles the spongin of the fibres of horny sponges. In sections of the choano- 

 some of var. carolae I have observed groups of highly stainable, oval cells 20- 

 30 long and 12-17 /< broad (Plate 2, fig. 7a). These cells are imbedded in 

 an alveolar tissue, composed of a mesh-work of elongated elements (Plate 2, 

 fig. 7b), and free from flagellate chambers. I am inclined to consider these large 

 cells as young ova. 



Skeleton. The ster raster-armour and the microscleres generally are well 

 developed, the megascleres somewhat rudimentary; not the megascleres of 

 the choanosome, but the hard sterraster-armour of the cortex, forms the main 

 support of the sponge. 



The megascleres are rhabds, simple teloclades, and a few multicladomal 

 and mesoclade derivates of the latter. The rhabds are for the most part blunt, 

 spindle-shaped, isoactine amphioxes. These pass on the one hand into pointed 

 amphioxes, on the other into cylindrical amphistrongyles or even amphityles. 

 Anisoactine blunt or pointed diactines and occasionally also styles and tylo- 

 styles are met with likewise. Some rhabds are rendered irregular by the presence 

 of small protuberances. Most of the teloclades are monaenes. Besides these 

 monaenes some cliaenes occur in var. carolae. These are more numerous in the 

 specimen from Charlotte Sound than in the specimen from Naha Bay. In var. 

 magaclada and var. megasterra monaenes only, the clades of which are much 

 longer in var. megaclada than in var. megasterra, are met with. Most of these 

 spicules are plagioclade, some orthoclade. 



These teloclades (teloclade-derivates) and rhabds are met with in all parts 

 of the choanosome. In its central parts the teloclades are relatively less nu- 

 merous than in its superficial parts. In the axial part of the choanosome of the 

 finger-shaped var. megasterra these spicules form a rather loose longitudinal 

 column or strand (Plate 1, fig. 21), from which single spicules and small spicule- 

 bundles extend towards the surface. These are arranged in a somewhat plumose 

 manner, abut obliquely on the sterraster-armour, and extend distally to the 

 limit between the cortex and the choanosome, or a little beyond it, in which 

 case they penetrate the proximal part of the sterraster-armour and terminate 

 witliin it. 



