TRANSACTIONS OF SECTION D. 619 



As to the nature of this unprecedented progress, it will suffice to consider the 

 Earthworms. In 1874 few were known to us. An advance in our knowledge, 

 which had then commenced, had made known but few more which seemed likely to 

 yield result. Darwin's book upon them had not appeared. Some were exotic, 

 it is true, but no one suspected that a group so restricted in their habits could 

 reveal aught beyond a dull monotony of form and structure. Never was surmise 

 more wide of the mark, for the combined investigations of a score of earnest 

 workers in all parts of the world have in the interval recorded some 700 odd 

 species of about 140 genera.^ Mainly exotic, they exhibit among themselves a 

 structural variation of the widest possible range. Not only do we recognise 

 littoral and branchiate forms, but others achsetous and leech-like in habit, to the 

 extent of the discovery of a morphological overlap with the leeches, under which 

 we are now compelled to remove them from their old association with the flat 

 worms, and to unite them with the earthworms. And we even find these animals, 

 as represented by the AcanthodrilideB, coming prominently into considerations 

 which involve the theory of a former antarctic continent, one of the most revolu- 

 tionary zoo- geographical topics of our time.*" 



This case of the earthworm may be taken as typical of the rest, since for each 

 and every class and order of animal forms, the progress of the period through which 

 we have passed since last we assembled here has produced revolutionary results. 

 Our knowledge of facts has become materially enhanced ; our classifications, at 

 best but the working expression of our ideas, have been to a large extent replaced 

 in clearer, more comprehensive schemes ; and we are to-day enabled to deduce, 

 with an accuracy proportionate to our increased knowledge of fact, the nature of 

 the interrelationships of the living forms which with ourselves inhabit the 

 earth. 



Satisfactory as is this result, it must be clearly borne in mind that its realisa- 

 tion could not have come about but for a knowledge of the animals of the past ; 

 and turning now to palaiontologry, it may be said that at the time of our last 

 meeting in this city the scientific world were just becoming entranced, by the 

 promise of unexpected results in the exploration of the American Tertiary beds, 

 then being first opened up. The Rocky Mountain district was the area under 

 investigation, and with this, as with the progress in our knowledge of recent 

 forms, no one living was prepared for the discoveries which shortly came to pass. 

 To consider a concrete case, we may premise that study of the placental 

 mammals had justified the conclusion that their ancestors must have had equal 

 and pentadactyle limbs, a complete ulna and fibula, a complete clavicle, and a 

 skull with forty-four teeth ; must have realised, that is, the predominant term of 

 the living Insectivora as generally understood. Who among the zoologists of 

 our time does not recall with enthusiasm the revelation which arose from the dis- 

 covery, during these early days, in the Eocene of Central North America, of the 

 genera at first described as Eo- and Helohyus ? '' The evidence of the existence, 

 in the locality named, of these forty-four toothed peccaries, as they were held to 

 be, rendered clearer the records of the later Tertiary deposits of the old world, 

 which were those of hogs, and, in correlation with the facts then known, 

 suggested that the Rocky Mountain area was the home of the ancestral porcine 

 stock, and that in Early Tertiary times their descendants must have migrated, 

 on the one hand, across the northern belt, of which the Aleutian Islands now mark 

 the course, into the old world, to beget, with complication of their teeth, the pigs 

 and hogs ; and on the other into Central South America, to give rise, with numerical 

 reduction of teeth and toes, to the peccaries, still extant. 



Migration in opposite directions with diversity of modification was the refrain 

 of this remarkable find, far-reaching in its morphological and zoo-geographical 

 effects. Nor can we allude with less fervour to the still more striking case of the 

 horses, indicating not merely a similar, though perhaps a later, migration, but 

 a parallehsm of modification in both the old and new worlds, culminating in the 

 latter in extinction, whereby it became necessary, on the advent of civilised man, 

 to carry back the old-world horse to its ancestral American home. No wonder 

 that this should have provoked our Huxley to the remark that in it we have the 



