70 ART. 1. — I. IJIMA : HEXACTINELLIDA, III. 



h being found and as yet none of the most highly developed 

 form c. AVith the growth of the sponge, a diminishes in number 

 and finally disappears altogether in the parenchyma, apparently 

 as the result of its transformation into b ; thougli it seems to 

 persist in the original condition in the basidictyonal plate. At 

 the same time, h in its turn is constantly developing into c, and 

 when this development is quite or nearly completed as in all the 

 larger specimens, the latter form becomes almost the only one 

 that is to be met wdth in the parenchyma. 



The second kind of hexasters constantly present in the species 

 may be called the sigmatocome (PI. IV., figs. 2 and 3; PI. V., fig. 

 11). Here we have to do with small and delicate-looking rosettes 

 measuring only 50-64 p- in diameter. In general shape and in 

 the proportion of parts they closely resemble Euplectellid flori- 

 comes, except in tliat each perianth of terminals is somewhat 

 more expanded and in that the terminals are conically pointed 

 at tlie outer out-flaring end instead of having toothed plates. 

 About a dozen or more, slender and distally gradually thickened 

 terminals spring in a single whorl fi'om the margin of a plano- 

 convex disc at the end of each moderately long principal. In 

 some rosettes, assumably those in an early stage of development, 

 both the principals and the terminals are considerably thinner 

 than in others. — The sigmatocome is found even in the smallest 

 specimens shown in PI. V., fig. 9, though not in so great abundance 

 as in all larger individuals. In these it is of common occurrence 

 in the parenchymal septa ; it occurs much less frequently in the 

 gastral layer also. On the surfaces of ]mrenchymal septa, it is 

 quite common to see the rosette shifted out to the tip of the free 

 ray of canalar oxyhexactins (PI. IV., fig. 8 ; PI. V., fig. 12), 



