64 Mr. G. P. Bidder. 



that part or tlie whole of one ray deviates at an angle of some 

 multiple of 60 from its normal course. That all deformities in these 

 species should be reducible to this law appears to me inexplicable on 

 the supposition that they are due to any biological variation of the 

 formative cells ; and it will be observed that the variation in which 

 two of the angles between the rays are of 60 is wholly irrecon- 

 cilable with the "honeycomb" theory of contiguous circles appealed 

 to by Minchin. Ebner (12) has worked out the relations of many 

 forms of spicule to the optic axis and the hexagonal prism : he sums 

 up against regarding the spicules as mere crystals. I can only claim 

 to have a little extended his observations, but that little is all in 

 favour of exact obedience to crystalline laws. 



Nitrate of potash has a crystalline form resembling almost to 

 identity that of calcite. Fig. 2 is copied from Lehmann (13) r 



FIG. 2. Nitrate of potash crystallising in caustic potash. (Copied from 

 Lehrnann (13), fig. 99.) 



and shows the form taken by nitrate of potash crystallising in the 

 presence of caustic potash. Fig. 3, placed near it for comparison, 



J 



K~J<*** v-i'xi ' i i 



5 3 . _ 



FIG. 3. Last remains of spicules ( x 1000) of Guancha coriacea, decalcified 

 slowly in glycerin. 



FIG. 4. Spicules of Clathrina clathrus ( x 1200) partly decalcified in glycerin. 

 The sharp truncation is conventional, to show that only part of the rays is 

 drawn. 



