DEVELOPMENT OF THE ANIMAL KINGDOM. 237 



urhcLy aquatic. The arrangement appears to be this — 

 the basis of each line is a series of marine forms ; the 

 remainder consists of a series designed to breathe the 

 atmosphere and live upon land, these being all of im- 

 proved organization. The classification which this sys- 

 tem implies may be said to be transverse to all ordinary 

 classifications. The invertebrate, ichthyic, reptilian, or- 

 nithoid, and mammalian characters are horizontal grades, 

 through which the lines pass, and where they send off 

 branches ; not separate and independent divisions. In 

 any of these branches where we have a clear knowledge 

 of the various forms, it is possible to trace the affinities, 

 in conjunction with an improved organization, through 

 genera which are adapted to a partially marine life, to a 

 residence in the mouths of rivers, or on shores and muddy 

 shallows, then through genera which are, in succession, 

 appropriate to marshes, jungles, dry elevated plains, and 

 mountains. And it is this series of external conditions 

 &nd adaptations which has caused that system of analo- 

 gies between various families of animals which has of 

 late attracted attention. But the immediate cause of the 

 development of each line through its various general 

 grades of being is to be sought in an internal impulse, 

 the nature of which is unknown to us, but which re- 

 sembles the equally mysterious impulse by which an in- 

 dividual embryo is passed through its succession of grades 

 until ushered into mature existence. Geology shows us 

 each line taking a long series of ages to advance from 

 its humble invertebrate effluents to its highest mamma- 

 lian forms ; and this I have ventured to call " the uni- 

 versal gestation of Nature." 



The traces of this order of the animal kingdom have 

 been seen in all ages of science. Every zoologist ac- 

 knowledges the gradations and affinities which appear 

 amongst animals. Prompted by what so palpably meets 

 observation, many have tried to range the various orders 

 or families in one line, or (to use the favorite phrase) 

 chain of being ; but they have always failed, which is 

 not to be wondered at. One cause why zoologists have 

 not up to this time thought of trying any different ar- 

 rangement, is the confusion arising from prevalence 

 amongst many families of parallelisms of structure, 

 which have been regarded as affinities, when in reality 

 they are only identical characters demanded by common 



