MATERIALS FOR A MONOGRAPH OF THE ASCONS. 553 



pass over this point for the present, however, and assume with 

 Dreyer that the first appearance of the sclerite takes place in a 

 node of the framework ; in other words, that the minute sclerite 

 has the value of a granule, and is to be classed as such. 

 Now the granules commonly found in protoplasm are very 

 variable, as has been said, in nature and consistency ; but they 

 always present themselves, whatever their size, as rounded 

 bodies of a more or less spherical form. In spite of their posi- 

 tion at the nodes of a framework, where, as Dreyer assumes, 

 they would be subject to " vesicular tension," no granules 

 have been recorded, to my knowledge, which show any approach 

 to the supposed primitive tetraxon form. If the sclerites have, 

 as a result of their position at the nodes of the framework, a 

 peculiar form and shape which all the other granules occupy- 

 ing the same position conspicuously lack, it follows that there 

 must be some other cause to produce this anomalous result 

 than their position simply. If vesicular tension cannot in any 

 other instance cause the granules at the nodes to assume a 

 tetraxon form, why should it do so in the case of the sclerites ? 

 If now we try to find a distinction between the sclerites and 

 the other granules which would account for their difference of 

 form, we can find none but the fact that the sclerites have, ex 

 hypothesi, a supporting or skeletal function. If, however, 

 their form be correlated not with their position, but with their 

 function, we are thrown back at once, as it seems to me, to 

 seek an explanation for the alleged primitive tetraxon, not in 

 the mechanical results of its position and origin, but in adap- 

 tation to its surroundings, — in fact, to just the theory 

 which Dreyer rejects. 



In any case there seems no reason why the sclerite should 

 have had a tetraxon form, unless it had at the same time a 

 supporting function. It is extremely probable, however, that 

 the material of which skeletons of any kind are built up 

 appeared at first as mere concretions, or perhaps excretions, — in 

 fact, as products, and perhaps as waste products, of the meta- 

 bolism, before they were utilised for any function. If such a 

 view be admitted, there is then no reason at all why the 



