STRUCTURE OE SUBERITES DOMUECULA. 243 



cellular protoplasmic network could be distinctly seen. The great interest of 

 the connective tissue, however, is its frequent modification into what may be 

 termed muscle-cells. Disposed in compact strands, specially abundant in certain 

 positions, these extended spindle-shaped cells certainly suggest a contractile 

 function. A thick layer occurs just below the ectoderm; numerous well- 

 defined, occasionally branching, strands run parallel to the surface somewhat 

 further inwards ; a similar compactness of disposition is very abundant 

 in the region adjoining the gasteropod shell, and lastly these muscle-strands 

 frequently occur round the larger canalicular passages. While the strands 

 of closely-packed spindle-shaped cells are quite definitely distinguishable, 

 evident transitions exist between the latter and ordinary connective tissue 

 cells (figs. 5-8). 



Reproductive Elements. — Embedded in the connective tissue matrix, I have 

 observed the occurrence of developing sperms in the form of morula-like balls 

 of minute cells, surrounded by an envelope of flattened connective tissue (fig. 

 11). These balls of cells correspond with the sperm-morulae described by 

 Schulze and Polejaeff. As ova occur in the same specimen, Suberites appears 

 to be hermaphrodite. The ova occur, frequently in extraordinary abundance, 

 throughout the whole sponge. In some cases two nuclei were present in the 

 ovum, or a nucleus with a stained aggregate at each pole, — probably the 

 beginnings of division. The chromatic contents of the germinal vesicle 

 exhibited a most varied appearance, which seems to me worthy of special 

 notice. Not one nucleolus, but several apparent nucleoli, were very generally 

 present ; a smaller spherule often seemed to arise as a bud from the larger, or 

 to lie adjacent to, though unconnected with it ; but more frequently three, 

 four, or five variously disposed nucleolid spheres of perfectly definite contour, 

 and uniformly stained, occurred. They were sometimes of equal size, but 

 oftener with one slightly larger than the others. An idea of the varied 

 disposition can be best obtained by a glance at a few nuclei represented in 

 fig. 10. My friend Dr Heider has observed a horse-shoe-shaped nucleolus 

 in sponge-ova, which might of course in cross section explain some of the 

 forms. A more complex form might obviously show several spheres on 

 cross section, and that this is the explanation is suggested by the nuclear sec- 

 tions in fig. 10, several of which were cut through the same nucleus at different 

 levels. It is also possible that we have here to deal with phenomena 

 resulting, not from the complicated shape of the nucleolus, but from the 

 occurrence of that multinucleolar condition which has, of late years, been 

 repeatedly observed. 



As Suberites is but ill-suited for minute histological study, which could in 

 such a form at most result in the confirmation of what can be better observed 

 in other types, I have contented myself with attempting to elucidate the general 



