66 T. IJIMA : HEXACTINELLIDA. I. 



dividual meshes. Structurally tlie beams are compact, though 

 the constitueut spicules are never in fusion. On their internal 

 surface are to be seen pores, which are the outlets of excurrent 

 canals ; for, tlie beams possess the chamber-layer, and the inflow 

 and outflow of Avater evidently take place here as well as in 

 the lateral wall. 



Observations on growing individuals corroborate F. E. 

 Schulze's view ('95, p. 25) with regard to the origin of new 

 beams and meshes in the sieve-plate. These arise by the split- 

 ting and shifting asunder, as it were, of the beams and nodal 

 plates already present. In other words, there arise in the tissues 

 gaps which gradually enlarge into new meshes. I have also seen 

 evidences of new beams, and therewith of new meshes, forming 

 themselves along the inner border of the cufl: 



Compared with the sieve-plate of U. renalis as figured by 

 F. E. Schulze (19'), that of E. 'wilder ialis presents on the whole 

 much larger meshes. 



Whereas the greater upper portion of the sponge-wall 

 possesses a certain degree of flexibility and elasticity, the lower 

 portion is firm owing to the fusion of the principal skeletal 

 elements in this region. As already mentioned, the lower end 

 of the body is well-nigh or quite destitute of the loose tissues ; 

 in fact it may be considered as dead. Some distance before the 

 extreme lower end of the skeletal tube is reached, the exposed 

 longitudinal bands of the rather coarse looking, anchoring fibers 

 begin to become frayed out inferiorly, soon to interlock among 

 themselves and to penetrate into the bulbous mud-ball that always 

 makes up the lower termination of the specimens. Not only the 

 basal tuft but also the lowest end of the internal skeletal tube 



