46 ANATOMY AND PHYSIOLOGY 



development ; and there is every appearance that they are 

 simply abortive developments of the larger and more perfect 

 organs, with which they always appear to agree in their 

 normal characters. 



There are two primary divisions of these forms of spicula, 

 — equi-anchorate, when both terminations are produced to 

 an equal extent, as in Figs. 140, 141 and 142, Plate VI, 

 and inequi-anchorate, when the distal termination is largely 

 and fully developed, while the proximal one is, compara- 

 tively, produced to a very limited extent, as in Figs. 137 

 and 138, Plate VI, each of these is subject to a certain 

 extent, to similar degrees of further diversity of form, 

 which may be designated bidentate, tridentate and 

 palmate. These forms are in truth but different degrees of 

 development of the normal palmate form ; but as we find 

 these variations constant in different species of sponges, it 

 is desirable that they should be separately designated, 

 as they afford excellent specific characters. Thus in 

 Haliclion3ria granulata, Bowerbank, we find large equi- 

 anchorate spicula, in which the lateral expansions of each 

 end of the curved shaft or bow which forms the palmate 

 terminations of the spiculum extend along the shaft towards 

 the middle of the bow, very little beyond the point of 

 curvature forming the basal commencements of the hooks ; 

 but although not decurrent on the shaft, the lines of the 

 inner margins are projected forward at an angle of about 

 45 degrees to the axis of the shaft; and as the outer lines 

 are projected in a corresponding degree, we have the palm 

 produced in the form of two concave conical teeth or palms 

 at each end of the spiculum ; and between these there is 

 not the slightest appearance of the ends of the hami, which 

 appear to be equally divided between the terminal palms or 

 teeth. This form I therefore term bidentate equi-anchorate.. 

 The same termination occurs among the inequi-anchorate 

 forms; and this mode of the development of the teeth 

 is well shown in the distal or larger portion of the bidentate 

 inequi-anchorate spiculum, represented in Fig. 137, Plate 

 VI. In other cases the termination of each hook does not 

 thus merge in the teeth, but is carried forward between 



