ADGUST26, 1898.] 



SCIENCE. 



255 



Crustacea, and (3) the myriopods and in- 

 sects. Of the third line Peripatus or a 

 Peripatus-like form was the earliest ances- 

 tor, which, of course, must have been ter- 

 restrial in habits, though its forebears may 

 have been some fresh- water leech-like 

 worm. We venture to state it is not wholly 

 impossible that so composite a type as Peri- 

 patus, which bears at least some of the 

 marks of being a persistent type, took its 

 rise on the continental land of the Precam- 

 brian. 



In the Precambrian time was also solved 

 the problem by the molluscs of producing a 

 spiral univalve shell ; for while a large pro- 

 portion of the Gastropoda were protected by 

 patella-like shells of simple conical form, 

 with these coexisted in the lowest Cambrian 

 forms with spiral shells, such as Platyceras 

 and Pleurotomaria. The comparative abun- 

 dance of those highly modified molluscs, 

 the Pteropoda, in the lowest or Olenellus 

 Cambrian strata, strongly suggests that their 

 diverence from the moi'e generalized gastro- 

 pod stem and their adaptation to a surface 

 or pelagic life must have taken place long 

 anterior to the dawn of the Cambrian.* 



With them must have lived a variety of 

 other surface forms besides Ehizopoda, 

 whose young served as their food. The 

 members of all classes of the Cambrian 

 were carnivorous, feeding on the proto- 

 plasm of the bodies of microscopic animals 

 or on the eggs and young of their own 

 species, some living on the bottom, and 

 others at the surface. Of marine plants of 

 the Cambrian there are but slight traces, 

 and it is evident that what there were were 

 restricted to the coasts and to s allow 

 water. The old idea that plants originally 



*Dr. Matthew has discovered at St. John, N. B., a 

 still lower and older bed, containing no Olenellus ; 

 bntForaminitera (OrbulinaandGlobigerina), sponges, 

 Pteropoda, Pelagiella which was probably an oceanic 

 Heteropod, very primitive branchiopods, with Ostra- 

 coda and six genera of trilobites. 



served as the basis of animal life must be 

 discarded. As at present no plant life ex- 

 ists below a few fathoms, a hundred per- 

 haps at the most, and since below these 

 limits the ocean depths are packed with 

 animal life which exists entirely on the 

 young or the adults of weaker forms, so 

 must the rise and progress of animal life 

 have been quite independent of that of 

 plants. The lowest plants and animals may 

 have evolved from some common bit of 

 protoplasm, some protist, but the evolution 

 of the animal types became very soon vastly 

 more complex. The specialization of parts 

 and adaptation to the environment were 

 more thorough and rapid in the lowest ani- 

 mals evidently in consequence of the 

 greater power of locomotion, and aggres- 

 siveness in obtaining food from living or- 

 ganisms, and the adaptability of animal 

 life to various oceanic conditions, especially 

 temperature, bathymetrical conditions and 

 a varying sea-bottom. 



This rapid differentiation and multiplica- 

 tion of different family, oi-dinal and class 

 ancestral types went on without those 

 biological checks which operated in later 

 times, when the seas and land masses of 

 the globe became more crowded. There 

 was a comparative absence of competition 

 and selection, this being due to the lack of 

 predaceous carnivorous forms to produce 

 that balance in nature which afterwards 

 existed. The two most successful and 

 abundant types were the trilobites and 

 brachiopods ; but the former were not es- 

 pecially aggressive in their habits, undoubt- 

 edly taking their food in a haphazard way 

 by burrowing in the mud or sand, having 

 much the same kind of appendages and the 

 same feeding habits as Limulus. The 

 brachiopods were fixed or burrowed in the 

 sand, straining the microscopic organisms 

 drawn into the mouth by the currents set 

 up through the action of their ciliated arms. 

 The most destructive and aggressive Cam- 



