98 PROCEEDINGS OF THE ACADEMY OP [1885. 



granted that we have but fragments of the primeval life, and these 

 fragments associated in a manner that cannot indicate the actual 

 life conditions. 



These earliest animals are mainly burrowing, crawling, or sta- 

 tionary forms. There is very little indication of the abundance 

 of swimming life which now crowds the ocean and must have 

 then done so. We find only minute swimmers, such as Pteropods 

 and Phyllopods, while if the Trilobites were able to swim it must 

 have been but a sluggish movement. There is no indication of 

 the existence of rapid and powerful swimmers. 



Yet there are several reasons for believing that swimming 

 animals existed in abundance. The rapid swimmer has an advan- 

 tage in food-getting and in escape from danger over the slow- 

 moving surface animals. Natural selection, therefore, must have 

 tended to produce swimming forms. 



The facts of embryology yield evidence to the same effect. 

 Nearly or quite all ocean animals begin life as swimmers. The 

 stationary forms become fixed only after their larval period is 

 passed. This fact indicates that at some early period the ances- 

 tors of our present fixed forms were free swimmers. 



But a stronger proof of this is found in the condition of the 

 animals whose fossil forms we possess. They are all covered with 

 protective armor. It is, indeed, to the preservation of this armor 

 that we owe our knowledge of their existence. We find no weapons 

 of offense. Everything is defensive. Even the trilobite, which 

 had nothing to fear from the other known forms, was clothed in 

 a strong coat of mail, and had acquired the habit of rolling him- 

 self into an impenetrable ball. There can be no question that he 

 had foes, stronger than himself, against whom he found defense 

 only in his chitinous armor. Yet of these predatory foes we 

 know nothing. 



All other preserved forms tell the same story. We would 

 know nothing of them but for their hard parts, and these hard 

 parts are all protective. The soft-bodied annelid saved itself 

 by burrowing in the mud. The mollusk clothed itself in a firm 

 limy covering. Of the remaining forms each wore some kind of 

 defensive armor. Many of them doubtless needed defense 

 against the trilobites, but the foes of the trilobite are missing. 



If we ascend higher in the rocks, the same tale is told. The 

 Hydrozoa, which had probably swum the earlier seas in forms 

 allied to our soft-bodied Medusae, become stationary and protected 

 as Graptolites. And simultaneously the powerful Cephalopods 

 make their appearance as surface forms, clothed in a heavy and 

 cumbrous defensive armor. If they formerly had mastery of the 

 seas, as we may conjecture, they had been driven from it by some 

 more powerful and rapid foe. 



In fact all the preserved forms may be looked upon as to some 

 extent degenerated types of life. They very probably represent 



