Evidence from Somatic Histogenesis 



51 



facts on which this statement is based. Although the prob- 

 lem of what all these spicules are for does not directly con- 

 cern us, indirectly it does, as the following further remarks 

 of Sedgwick will indicate. "While it is pretty clear," he 

 says, "that the main function of the skeletal structures is 

 the support and protection of the sponge body, it is by no 

 means easy to give explanations of the diversity and com- 



FIGURE 48. SPICtJLES OF SPONGES (AFTER LAXKESTER). 



plexity of form which they present. The form of the megas- 

 cleres is probably connected with the form of the canal sys- 

 tem with which they are in relation (F. E. Schulze) ; but the 

 form and even the existence of the microscleres defies any 

 reasonable explanation." And then comes this statement, 

 highly significant for almost any discussion of heredity: 

 "By some spongologists the small spicules are regarded as 

 functionless, and as having on that account a greater value 

 for classificatory purposes." 13 



If any one wishes to be convinced of the extent to which 

 the spicule forms differ with different species, he should 



