136 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



region, differ from those more deeply situated in having some- 

 what longer principals and slightly more slender terminals. 

 Moreover, tlie former generally show a greater total number of 

 terminals, being usually normally developed, although hemihexact- 

 inose and hexatinose forms may be common among the latter. 

 (Compare in PI. XXI., figs. 4 and 5 with figs. 6-8 ; in PL XXII., 

 figs. 7 and 8 with figs. 14 and 15). It must however be borne 

 in mind that between the peripheral and the more deeply located 

 oxyhexasters there is always a gradual transition within one and 

 the same sponge. 



Of the three oxyhexaster-forms occurring together in a 

 species, it is usually the hexactinose amongst which are found 

 individual oxyhexasters with greatest diameter or axial length, — 

 a fact which I have noticed also in some Rossellinae. It appears 

 as if the reduction in the number of terminals to the minimum, 

 i.e., to one to each principal, in a measure fivors the growth of 

 the spicule in general size. 



In a number of the species I have specially gone into the 

 observation of the axial cross in hexactinose oxyhexasters. With 

 a little trouble I have found it in all cases an easy matter to 

 demonstrate what I have repeatedly emphasized as to the extent 

 of the axial filaments in the central parts of that oxyhexaster 

 variety. For the rest I may let fig. 2.">, PL XIV., speak for 

 itself. By the side of that figure is another (fig. 24) showing, 

 for the sake of comparison, the extent of the axial cross in the 

 central part of a normal oxyhexaster in which each principal is 

 supplied with two terminals. 



It scarcely needs to l:»e reiterated that uniterminal principals, 

 irrespective of their occurrence in a hemihexactinose or in a 

 hexactinose oxyhexaster, are joined to their single terminal mostly 



