270 TOWARDS THE HUMAN FORM 



dimensions, seem to have been the ancestors of the Dinosaurs, 

 to which they passed on various peculiarities of skull-formation, 

 and particularly the construction of the palatal vault. But if 

 the physiological mechanism is clearly apparent that has 

 turned crawling Reptiles into Reptiles that walk and leap, 

 and if it has been possible to reconstruct at great intervals 

 some of the steps in this evolution, the series of stages covered 

 is broken nevertheless by enormous gaps. We can see that 

 any such reconstruction will be difficult. Many of these 

 cryptogenous beasts appear almost simultaneously at parts of 

 the globe so widely separated from one another that we find 

 some difficulty in admitting that an}^ means of communication 

 existed easy enough to allow such heavy animals, probably 

 sedentary in their habits, to cover such great distances. Forms 

 that vary but slightly from the Triassic genera, Zanclodon and 

 the Megalosaurians, for example, are found in Europe and the 

 United States, which both formed part of the North Atlantic 

 continent, and also in the southern parts of Africa and in India, 

 which at that time formed part of the Gondwana continent. 

 Morosaurus, Ccelurus, Stegosaurus, Camptosaurus, Triceratops, 

 and Hadrosaurus are represented sometimes by different species 

 in Europe and the United States, that is to say, at the 

 two extremities of the North Atlantic Continent, during the 

 Jurassic and Cretaceous Periods. Although these periods lasted 

 long enough to admit of the lengthiest journeys into the interior 

 of a single continent, this wide distribution remains remark- 

 able, and it is incredible, in any case, that such migrations took 

 place between Gondwana and the North Atlantic Continent. 

 We must admit, therefore, that similar forms may have arisen 

 separately, which confirms the view that constant natural 

 forces acting upon organisms which at first differed but little 

 from one another, as the early Batrachians must have done, 

 have independently produced analogous organic series in 

 widely separated regions of the globe. That is equivalent to 

 saying that the same causes acting in similar conditions always 

 produce the same effects. This is an elementary truth well worth 

 remembering in the domain of natural science, where the idea 

 of capricious and independent creations reigned for so long. 

 The parallel evolution of the herbivorous and carnivorous 

 Dinosaurs shows, moreover, how weak was the principle of the 

 correlation of forms and the subordination of characters upon 



