E. .MARSHALL!. — SPICULATION. 101 



parts of the sponge but are confined to the external trabecular 

 region under tlie laj'er of dermal paratangentials. The principal 

 rays (fig. 20) are about 7'/o « long as measured from the spicular 

 center ; the surface shows minute tubercles ; the disc at their 

 distal end is, on the outer surface, densely beset with the thickened 

 bases of rhaphidial terminals. "When the latter fall off, as they 

 seem to do by a normal pliysiological process, the bases remain 

 to the disc as small spiny processes (fig. 20). It is of very frequent 

 occurrence that one meets with the relics of graphiocomes after 

 the complete or partial loss of the terminals or rhaphides. These 

 attain a length of llo « when fully developed. 



Free rhaphides are found among the trabeculae in considerable 

 quantities, either irregularly scattered or still grouped in sheaves 

 and often under such circumstances of relative position to graphio- 

 come-relics as put the original connection of both beyond the 

 reach of doubt. They seem to be moved on towards the surface, 

 becoming on the way so directed as to point outwards with one end, 

 and finally to mostly arrange themselves in a bundle-like manner 

 along and around each hilt-ray of the dermalia (PI. V, fig. 36). 

 In no other species that I have studied were the rhaphides so 

 constant or abundant in the position just mentioned. The com- 

 monness, even in old individuals, of the source of rhaphides, i.e., 

 the graphiocome, indicates that these fine needle-like spicules are 

 being constantly thrown out from the sponge surface, in all prob- 

 ability as a sort of defensive missile. 



The account of developmental facts with regard to the above 

 three kinds hexasters, I will defer until I shall have completed 

 the histology of the soft parts. 



As the fourth kind of hexasters present in £. marshaUi, I 



