REVIEWS 787 



Protodonata— intermediate between the still more primitive Palaeodictyoptera of 

 the Carboniferous and the modern Odonata, or dragon-flies. 



In this connection reference may be made to a marked defect in the book, 

 namely that the index does not include groups of higher rank than genera, and 

 that when mention is made in the text of groups other than those under considera- 

 tion no reference is made to the pages where they are respectively described. In 

 this particular instance, for example, the group Palaeodictyoptera is mentioned on 

 page 809, but we have to search through the fourteen preceding pages before there 

 is any possibility of finding out what insects it represents. And such waste of 

 time is trying to the temper ! Moreover, is it not too absurd to spell such names 

 as Pakeodictyoptera with a diphthong in the second syllable and Palaeontology 

 and Palaeozoic without it ? 



Reverting to the giant dragon-flies of the Carboniferous, it is mentioned that 

 in Meganeura mo?iyi, the largest of them all, the wing-expanse is no less than 

 75 centimetres ; but it would have been well if some reference had been made 

 to recent speculations with regard to the physical conditions necessary to enable 

 such monsters to fly, which, like the giant pterodactyles of a later epoch, they could 

 not apparently have done if they lived under conditions of atmospheric pressure 

 similar to those existing at the present day. 



In the Introduction, which contains an excellent summary of the stratigraphical 

 sequence of rocks and a review of ancient and modern theories with regard to the 

 origin, evolution, and extinction of species, attention may be particularly directed 

 to the following thoughtful passage : " For the extinction of many plants . . . 

 and animals ... of former periods no adequate explanation has yet been found. 

 Changes in external conditions, especially such as regards the distribution of land 

 and water, climatal conditions, saltness of the water, volcanic eruptions, paucity 

 of food-supply, the encroachments of natural enemies, and diseases, may have led 

 to the extinction of certain forms, but such suggestions signally fail to account for 

 the disappearance of an entire species or particular groups of organisms. Often- 

 times extinction seems to have been caused merely by superannuation. Long- 

 lived forms belong for the most part to persistent types whose range of species is 

 limited. Their reproductive functions have declined, and, like an individual in its 

 senescence, they evince the symptoms of decrepitude." 



Palaeontology, we may observe in conclusion, has been decried as an obsolete 

 and unnecessary science, which ought to be merged in zoology and botany. But 

 there are many and cogent reasons against such a view, not the least of these 

 being a volume like the one before us, which is very nearly the ideal of what a 

 manual of palaeontology should be, and which displays before the eyes of the reader 

 a cinematographic sketch of the past history of a portion of the animal kingdom, 

 the vividness and compactness of which would be utterly and completely lost if its 

 contents were amalgamated with a volume on recent zoology. 



R. L. 



Problems of Genetics. By William Bateson, M.A., F.R.S. [Pp. ix + 258, 

 illustrated.] (Yale University Press. London : Humphrey Milford, Oxford 

 University Press, 1913. Price 17s. net.) 



Certainly it would be a misfortune to the advance of science were Darwinism 

 established as an orthodoxy against which a biologist should write only at the 

 peril of his reputation, and were the writings of Darwin accredited with a plenary 

 inspiration. It would be even more paralysing were the principles expounded by 



