IX] ANL SPICULAR SKELETONS 673 



subject, which is certainly no small nor easy one, it may conduce 

 to simplicity and to brevity if we make a rough classification, by 

 way of forecast, of the conditions we are likely to meet with. 



Just as we look upon animals as constituted, some of a great 

 number of cells, others of a single cell or of but few, and just as 

 the shape of the former has no longer a visible relation to the 

 individual shapes of its constituent cells while in the latter it is 

 cell-form which dominates or is actually equivalent to the form of 

 the organism, so shall we find it to be, with more or less exact 

 analogy, in the case of the skeleton. For example, our own skeleton 

 consists of bones, in the formation of each of which a vast number 

 of minute ll.ing cellular elements are necessarily concerned; but 

 the form and even the arrangement of these bone-forming cells or 

 corpuscles are monotonously simple, and give no physical explana- 

 tion of the outward and visible configuration of the bone. It is as 

 part of a far larger field of force — in which we must consider gravity, 

 the action of various muscles, the compressions, tensions and 

 bending moments due to variously distributed loads, the whole 

 interaction of a very complex mechanical system — that we must 

 explain (if we are to explain at all) the configuration of a bone. 



In contrast to these massive skeletons we have other skeletal 

 elements whose whole magnitude is commensurate with that of a 

 living cell, or (as comes to very much the same thing) is comparable 

 to the range of action of the molecular forces. Such is the case 

 with the ordinary spicules of a sponge, with the dehcate skeleton 

 of a radiolarian, or with the denser and robuster shells of the 

 foraminifera. The effect of scale', then, of which we had so much 

 to say in our introductory chapter on Magnitude, is bound to be 

 apparent in the study of skeletal fabrics, and to lead to essential 

 differences between the big and the Httle, the massive and the 

 minute, in regard to their controlling forces and resultant forms. 

 And if all this be so, and if the range of action of the molecular 

 forces be now the important and fundamental thing, then we may 

 somewhat extend our statement of the case, and include among our 

 directive or constructive influences not only association with the 

 living cellular elements of the body, but also association with any 

 bubbles, drops, vacuoles or vesicles which may be comprised within 

 the bounds of the organism, and which are (as their names and 



