160 T. IJTMA : HEXACTINELLTDA. I. 



concerning the size of the nuclei in the trabecala? Avill explain 

 itself. It is also plain that, if there prevails a general uniformity 

 of size and appearance among all the nuclei, which I hold to he 

 the case, the assumption of the identity of this or that kind of 

 cells with another should lose all its validity, so long as it is 

 founded on the similarity of their nuclei alone. 



Finally I will mention here, reserving the details of my 

 observations relative to the point to another chapter, that the 

 thesocytes seem to he one of those kinds of cells which arise directly 

 from the archreocytes, the transformation being effected simply 

 by gradually accumulating the 'Knollen' in the cell-body (PI. 

 IV, fig. 24). It may perhaps be urged that the archseocytes may 

 be present in some species with, and in others without, the cell- 

 outlines, and that the size of the nuclei may likewise be a vari- 

 able matter ; but the fact would remain the same that the theso- 

 cytes — the 'Knollen ' cells of S. arch'ca included— develop out of 

 the ' larger nuclei ' of Schulze. 



To resume my <nvn account of the trabeculse. I have said 

 in effect that these consist of a fused cytoplasm or nucleated 

 protoplasm (syncytium) in the form of threads and membranes. 

 It will be noticed that here recur in a measure the old sarcode- 

 theory, O. Schmidt's ('64), of the sponge ground-substance, and the 

 syncytium-theory, Haeckel's ('72), of the ' exoderm ' in calcare- 

 ous sponges. Whatever fate these theories may have met in the 

 case of other sponges, in the Hexactinellids ihey may be said to 

 have preserved a certain degree of applicability. As regards 

 the general soft tissue of the Ilexactinellida in particular, there 

 were among the older investigators some who termed it the 

 ' sarcode ' (Thomson, '68 à '70 ; Kent, '70) or ' sarcodine ' (Mar- 



