66 W. WOODLAND. 



though of ten also symmetrical structures like bones, feathers, 

 and the like is the assertion necessarily implied in the suppo- 

 sition that the forms of spicules are inherited. 



Another very important difference distinguishing spicules 

 from other cell-deposits relates to their disposition in the 

 organism. Apart from the fact already sufficiently insisted 

 upon that all hard deposits save spicules (not those of 

 Eadiolaria) arise in cells connected with the rest of the 

 organism, there is the additional significant fact that all 

 (except concretions and crystals) these non-spicular deposits 

 (bones, teeth, nails, hairs, scales, feathers, etc.) are, on 

 account of the connection of the secreting cells with the rest 

 of the organism, usually laid down (obviously by inheritance) 

 only in those particular parts of the organism where they 

 are required, the appendicular skeleton, e.g. being formed 

 in the axes of limbs where the greatest stresses exist, dermal 

 bones protect particular viscera in particular places, nails 

 occur on the terminal phalanges where most contact occurs, 

 and so on. Spicules, on the other hand, are not limited in 

 their distribution in this manner, but tend to occur wherever 

 the purely physical conditions permit the wandering cells to 

 secrete them (calcareous spicules, e.g. cannot occur in the 

 vicinity of digestive or other organs where acid solutions 

 abound), and their local adaptations in form to the archi- 

 tecture of the organism are, there is good reason to believe, 

 determined by purely physical causes which influence the 

 scleroblasts duriug the development of the spicule. 



In view, then, of the above arguments, which, collectively, 

 are, in my opinion, of considerable weight, and, in the 

 absence of direct proof to the contrary, we are, I think, for 

 the present justified in declining to entertain the hypothesis 

 of the inheritance of spicule forms. The hypothesis of the 

 inheritance of spicule forms, it is true, does not necessarily 

 imply that such forms have arisen by the process known as 

 natural selection ; natural selection, as even the most ardent 

 selectionists admit, is obviously incompetent to account for 

 the complex symmetry of spicule forms. The hypothesis 



