4 ART. 1. 1. IJIMA : HEXACTINELLIDA, III. 



referred to, is a much coarser structure and exhilnts nieslies of 

 a rectangular, trapezoidal, triangular or irregular shape. Within 

 a larger mesh bounded l)y the stronger beams are inclosed smaller 

 meshes formed by the weaker beams, and all the hypodermal 

 meshes, large and small, are alike overspread by the dermal 

 (or autodermal) layer already described, similarly as in certain 

 Rossellids, Caulophacids, etc. While weaker hypodermal beams 

 appear as simple spicular bundles, stronger ones are in the form 

 of laterally compressed bands. The latter, at the points of 

 junction with the choanosome, expand into vertical plates, which 

 go to form irregular pillars. 



The frontal lattice evidently gives suj)port to the ectosome only. 

 It thus differs sharply from the sieve-plate of Eujüectella or of 

 Hyaloneiiia^ which structure, in my 023inion, is a peculiarly 

 modified part of the sponge-wall in its entire thickness and 

 therefore contains not only the ectosome but also the choanosome 

 (Contrib. L, pp. 38, 66). Moreover, while a sieve-plate always 

 stands in connection with either the principal or the sole place 

 of water exit, it is just the opposite with the frontal lattice, which 

 is developed apparently for facilitating the inflow of water. 



Nowhere else is the subdermal space so distinctly and spacious- 

 ly developed as under the frontal lattice, which fact contributes 

 not a little to the peculiarity of this side. It is especially deep 

 (10 mm. or more) in the middle. In conformity with the wide 

 subdermal space, many of the incurrent canals leading from it 

 are large, some measuring VI mm. across at the entrance. 



The peripheral border of the frontal lattice may practically be 

 considered to coincide with the marginal edge of the body, though 

 at certain parts where this is rounded, it may not reach up to, 

 but stops a greater or less distance short of, the ridge-line. In 



