REVIEWS 715 



Water Reptiles of the Past and Present. By Prof. S. W. Williston. 

 [Pp. vi + 251, with 131 illustrations.] (Chicago: The Cambridge University 

 Press, 1914. Price 12s. net.) 



The first vertebrates were undoubtedly marine forms perhaps allied to the primi- 

 tive cartilagenous fish. After the great step forward had been taken and the 

 Amphibia and Reptiles had become land dwellers with habits and structure adapted 

 to their environment, some of them returned to the water either fresh or salt and 

 consequently had once again to become adapted to changed surroundings. The 

 same return to the water has also taken place in certain of the mammals, and the 

 whales and porpoises of to-day are undoubtedly the highly modified descendants 

 of land-dwelling mammals. Prof. Williston furnishes a very instructive and 

 interesting account of the various branches of the class Reptilia both recent and 

 extinct that have come to live in the water either partially or completely. 



It would perhaps be natural to suppose that the necessary structural adjustments 

 could be made by the re-assumption of some of the features of their remote marine 

 fish-like ancestors. Indeed a glance at the spirited restoration of an Ichthyosaur 

 on p. 108 will suffice to show how readily one could accept such an explanation 

 unless the details of its structure were more closely studied. Their discoverer 

 Scheuzer held them to be fish, and the name Ichthyosaur was later given to the 

 genus to indicate that they were intermediate between fishes and reptiles. One 

 fact however appears to be consistently borne out by anatomical and palasontological 

 inquiries, and that is that structures that have once been definitely lost in the past 

 history of a race cannot be reacquired and consequently when wanted again their 

 place has to be taken by new structures or a modification of existing ones. Such 

 new organs may resemble superficially those of remote predecessors, but a closer 

 examination will show them to differ anatomically. This resemblance brought 

 about by the similar needs or environment of the organisms is termed homoplasty 

 or convergence and is a very interesting phenomenon. At times the convergence 

 is not limited to one or two organs, but the whole body form of the animal is 

 influenced, as for example the fish-like appearance of the Ichthyosaurs, whose 

 general shape is again reproduced by the Dolphins. This likeness does not in 

 any way indicate a relationship between the forms possessing it, but is due to a 

 similarity of habits and surroundings. Many striking examples of convergence are 

 illustrated in this work. 



Although dealing only with the modifications adapting reptiles to partial or 

 complete aquatic life, it is remarkable how many different forms come within the 

 scope of its pages. With some of the modifications, exemplified by turtles and 

 crocodiles, we are already familiar, and the many others, mostly fossil, are to be found 

 in this book. The descriptions are clear and easily followed, and the introductory 

 chapters call attention to the main points of reptilian structure and classification 

 relevant to the subsequent pages. The accounts are quite up to date, and even 

 although it is meant to have a more or less popular appeal we think the value of 

 the book would have been augmented by the addition of a short bibliography. 

 The short historical introductions to some of the chapters are very interesting, 

 especially the account of the vicissitudes undergone by the first known fossil skull 

 of a Mosasaur. The book forms a useful addition to the few volumes that make 

 the results of recent palaeontological research accessible to the general reader. 

 It is well illustrated and printed. 



C. H. O'D. 



