100 PROCEEDINGS OP THE ACADEMY OF [1885. 



organic functions are certainly not all of primitive origin. Many 

 of them may have been the product of ages of slow development. 

 Such may have been the case with the development of glands suit- 

 able for the secretion of chitin, carbonate of lime, and the other 

 protective substances. We know that it was at a late date in the 

 history of life when animals first began to secrete an internal 

 hard skeleton. The need of protection undoubtedly caused a 

 more rapid evolution of the power to secrete an external hard 

 covering, and yet life may have long prevailed before this 

 adaptation was gained. The mantle of the bivalve mollusks, for 

 instance, with its glands for the secretion of a limy shell, cannot 

 have been a primitive feature of molluscan life. So the chitin- 

 forming glands of the crustaceans may have been a late product of 

 evolution. It is possible that, in the early days of life, all the 

 mineral ingredients of food were directly excreted. It is equally 

 possible that the power of transforming food elements into hard 

 substances did not exist. The development of dermal glands, 

 necessary to the secretion of external skeletons, teeth, etc., must 

 have occupied a considerable time, and its completion may have 

 taken place but shortly before the opening of the Cambrian 

 period. 



If such was the case, the preceding life must have been of a low 

 order, and of small dimensions. Animals might have grown to 

 considerable size with cartilaginous skeletons, but scarcely without 

 teeth or other hard weapons of offense, of which no trace remains. 

 It may be that the earlier forms of life were in great part swim- 

 ming animals, that they waged constant war upon each other, and 

 that in time, through the action of natural selection, the power of 

 secreting defensive armor was evolved.. As this armor grew 

 denser and heavier the swimming powers became abridged, and 

 the armored animals were successively carried to the bottom, and 

 forced into slow-moving or stationary habits of life. 



In corroboration of this idea is the fact that the power of 

 secreting an internal skeleton appeared only at a much later date. 

 It has never been developed in the Invertebrates, except in late 

 cephalopods, and in all these animals the external armor has 

 necessarily been utilized for muscular attachment. The superi- 

 ority of the vertebrates is largely due to the fact that their 

 muscular attachment has alwa3's been internal, a method which 

 gives much greater flexibility and power of movement. Yet for 

 a long period after the appearance of vertebrate life the basis of 

 muscular attachment was merely a rod of cartilage. Even the 

 great Devonian fishes, with their dense epidermal plates, were 

 destitute of internal bone, except that in a few cases they possessed 

 ossified vertebral arches. The next evidence of power to secrete 

 internal bone is found in certain Carboniferous Ganoids, which 

 possessed a mere ring of bone in the external portion of their 

 vertebrae. It cannot reasonably be argued that bony skeletons 



