226 DR. J. MURIE 01NI STEERE'S SPONGE, 



2. Acerate spined Spicula (figs. 17, 18, and 19). — These are of two sizes, large and 

 small. Both sorts are long, acerate, fusiform, inequilateral, one half heing thicker than 

 the other. The thicker moiety is rather more abruptly pointed than is the attenuated 

 one. The larger-sized spicula average yq inch long by g^ inch at their thickest part. 

 The smaller acerate spicula in most respects agree with the preceding, but are not more 

 than one fourth or one fifth the size of the others. More frequently I have met with 

 them as represented (fig. 19), in bundles, whereas the larger spicula are usually single and 

 apart when obtained. The spines covering the large spicula (very manifest in fig. 18) 

 point away from the thick end, and they all slope in the same direction, closely applied 

 and almost parallel with the shaft. Each spine is simple, smooth, and conical, supported 

 on a projecting basal portion of the shaft. These acerate spined spicula, and particularly 

 the big kind, may be regarded as subskeletal, being situate throughout the structure of 

 the sponge, though chiefly towards the surface. They appear to be a very common form 

 among the Hexactinellid sponges. 



According to Mr. Carter, when elongated they apparently pass into the anchoring 

 spined spicules of the bearded species of the Hexactinellida. Moreover such spicula he 

 regards as " subskeletal," because he avers they are often drawn into the vitreous fibre, 

 with which they become indistinguishably incorporated during life ; he even holds that 

 the larger scopuline spicules, presently to be described, are occasionally similarly amal- 

 gamated. 



3. Beopuline Spicula (figs. 13 to 16).— Two forms of these obtain, likewise differing 

 in dimensions, (a) The larger of the two spicula (fig. 13) consists of a straight shaft and 

 terminal arms from two to four in number. The shaft is microspined, inflated and pointed 

 at the free extremity, and the opposite end terminates in a palmate, bifid, or quadrangular 

 inflation, springing therefrom two to four and occasionally five arms. These latter are 

 opposite, extended fork-like almost in a line with the shaft itself, and are microspined 

 and indistinctly capitate, or with convex head. The shaft of these large scopuline spicules 

 is -£g inch long, and the arms t^qo incn lon g- ( b ) Tlie smaller scopuline spicula 

 (fig. 15) have also a straight shaft and from two to four terminal arms. They differ from 

 (a), besides size, in the arms being opposite and expanded laterally or flower-like. Both 

 shaft and arms are microspined, the arms very indistinctly capitate. In dimensions these 

 second kind of scopuline spicules have a shaft y^g- inch long, the arms y^ inch long. 

 Besides their terminal arms, both kinds of the spicula under consideration are often more 

 or less provided with shorter armlets, which spring from the body of the shaft at right 

 angles, and vary in number as well as in length (figs. 14 & 16). While they are often 

 hardly traceable in the large scopuline form («), they on the other hand are occasionally 

 profuse in the smaller kind (5), numbering in the latter frequently as many as twelve, 

 which usually are longest towards the middle of the shaft. These different figured sco- 

 puline spicula pass by almost imperceptible gradations into each other, though in most 

 slides under the microscope the two sorts are readily distinguished even when lying in 

 heaps, as is shown in fig. 11. 



Mr. Carter remarks that the said scopuline spicula belong to the sarcode inside the 

 dermal meshwork, where their original arrangement has been destroyed by the contracting 



