PROF. MARSH ON MAMMALS. 7 1 



principles were useful guides as to the probable nature of the 

 ancestral mammal ; in the present imperfect state of the palaeonto- 

 logical record he preferred to commence by working backward 

 from the well known comparatively recent forms. In the first 

 place, mammals possess the power of rapid adaptation to their 

 conditions of life. There have been four main centres of adaptative 

 radiation, of which the best case is that of Australia, where the 

 marsupials have acquired forms which among placental mammals 

 are divided between different orders. The starting point of each 

 adaptative radiation has been a small, unspecialized land mammal. 

 Finally it is probable that the ancestral mammal was insectivorous 

 or omnivorous. Remembering these principles we can trace the 

 line of mammalian descent backward ; it leads us to the Jurassic, 

 when the mammals were all small and belonged to three groups — 

 the primitive insectivores, which have been regarded as marsupials, 

 although there is no evidence to support that view ; second, the 

 Multituberculates, which are probably early Monotremes ; third, 

 the Marsupials. Reversing the order of enquiry, Professor Osborn 

 then referred to the fact that in the Permian there are three groups 

 of reptiles, one of which is surprisingly mammalian in some of its 

 characters, and tempts us to connect the herbivorous section of 

 anomodonts with the monotremes. He thought, however, that the 

 many striking points of resemblance between these reptiles and 

 mammals were due to parallelism, similar characters having been 

 independently acquired. He agreed with Professor Seeley that 

 the known anomodonts are not the direct ancestors of mammals, 

 but are a collateral line. But he disagreed when Professor Seeley 

 sought for a much earlier common ancestor of the mammals and 

 the anomodonts, for he believes that an undiscovered and less 

 specialized third sub-group of anomodonts will be found to be the 

 true ancestor of the mammals. The chairman, however, has shown 

 that the mammalian egg is amphibian rather than reptilian in 

 cliaracter ; and if much weight is to be laid on this point, then the 

 mammals may have descended from some reptile which retained 

 certain amphibian characters. 



Professor MARSH said that the question under discussion is not 

 new, but one of a series of similar nature and difficulty. The origin 

 of Birds, of Reptiles, of Amphibians, and of Fishes really precede 

 it, and offer less difficulties in solution. The answer to each, in my 

 opinion, belongs to the future, and how far it may profitably be 

 sought in the present limited state of our knowledge is a fair 

 question in itself. 



Too often in the past, a discussion on the origin of Mammals 

 has seemed a little like the long philosophico-theological contro- 

 versies in the middle ages about the exact position of the soul 

 in the human body. No conclusion was reached, because, for one 

 reason, there were no facts in the case that could settle the question, 



