1896.J ^^ [Bailey. 



of their existence, these organisms are amcebi-like, that is, animal-like, 

 but at another stage they are spnriferous or plant like. The initial diver- 

 gencies in organisms were no doubt concerned chiefly in the methods of 

 appropriating food, the animal-like organisms apprehending their food at 

 a more or less definite point, and the plant-like organisms absorbing food 

 throughout the greater or even the entire part of their periphery. It is 

 not my purpose to trace the particular steps or methods of these diver- 

 gencies, but to call your attention to what I believe to be a fundamental 

 distinction between the two lines of development, and one wliich I do 

 not remember to have seen stated in the exact form in which it lies in my 

 mind. 



Both lines probably started out with a more or less well-marked circu- 

 lar arrangement of the parts or organs. This was consequent upon the 

 peripheral arrangement of the new cells in the development of the mul- 

 ticellular organism from the unicellular one. A long line of animal life 

 developed in obedience lo this peripheral or rotate type of organization, 

 ending in the echinoderms and some of the mollusks. This line long ago 

 reached its zenith. No line of descent can be traced from them, accord- 

 ing to Cope. The progressive and regnant type of animal life appeared 

 in the vermes or true worms, forms which are characterized by a two- 

 sided or bilateral, and therefore more or less longitudinal, structure. The 

 animal-like organisms were strongly developed in the power of locomo- 

 tion, and it is easy to see that the rotate or centrifugal construction would 

 place the organism at a comparative disadvantage, because its seat of sen- 

 sation is fartliest removed from the external stimuli. But the worm- like 

 organisms, "being longitudinal and bilateral," writes Cope, "one ex- 

 tremity becomes differentiated by first contact with the environment." 

 In other words, the animal type has shown a cephalic, or head-forming, 

 evolution in consequence of the bilateralism of structure. The indi- 

 vidual has become concentrated. Out of tliis vvorm-form type, theie- 

 fore, all the higher ranges of zootypic evolution have sprung, and one is 

 almost tempted to read a literal truth into David's lamentation that "I 

 am a worm and no man." 



If, now, we turn to plants we find the rotate or peripheral arrangement 

 of parts emphasized in all the higher ranges of forms. The most marked 

 bilateralism in the plant world is amongst the bacteria, desmids, and the 

 like, in which locomotion is markedly developed ; and these are also 

 amongst the lowest plant types. But plants soon became attached to the 

 earth, or, as Cope terms tliem, they are *' earth parasites." They there- 

 fore found it to their advantage to reach out in everj' direction from their 

 ^upport in the search for food. Whilst the centrifugal airrangement has 

 strongly tended to disappear in the animal creation, it has tended with 

 equal strength to persist and to augment itself in the plant creation. Its 

 marked development amongst plants began with the acquirement of ter- 

 restrial life, and with the consequent evolution of the asexual or sporo- 

 phytic type of vegetation. Normally, the higher type of plant bears its 



PUOC. AMEK. PHILOS. SOC. XXXV. 150. L. FEINTED JULY 7, 1896. 



