66 ART. 1. 1. IJIMA : HEXACTINELLÎDA, III. 



axial length. Rays thin, smooth throughout, gradually attenuat- 

 ing, nearly straight or slightly bent. One of the rays always 

 stands out freely from the septal surface, and ^Y]lere the septum 

 is not sufficiently thick to inclose the entire length of the opposite 

 ray, this may also project from its other surface to a greater or 

 less extent. As before indicated, a sharp distinction can not be 

 drawn between the canalaria and the hexactinic parenchymalia. 



The hexasters are, broadly speaking, of two kinds, viz., disc- 

 ohexasters and sigmatocomes. 



The discohexasters occur in abundance everywhere in the 

 body except in the dermal layer. Of them I may distinguish three 

 varieties or forms which I shall designate with the letters a, h 

 and G. All these mero'e into one another throueh forms of in- 

 termediate shapes and sizes. They occur in different quantitative 

 proportions and also show certain differences in the manner of 

 relative distribution in the body, according to the size of the sponge. 

 As will directly be more fully pointed out, the three forms seem 

 to represent in a great measure different developmental stages of 

 one and the same kind of discohexaster, — stages passed through 

 by it during the post-larval growth of the sponge. Hence it may 

 happen that a quite young sponge lacks discohexasters in the 

 older phase of their development, and that a mature one, on the 

 other hand, is either wanting in those representing their younger 

 phase or shows these in but a limited number ; whereas, all the 

 developmental phases are numerously and constantly met with in 

 individuals of certain intermediate ages. 



Form a, to begin with that discohexaster-phase which seems 

 to represent the earliest stage of development, comprises the 

 smallest discohexasters of the species. Diameter, commonly 100- 



