REVIEWS 185 



The statement on p. 77 that "the right systemic arch gives off the carotid 

 artery, which in many snakes — the common grass-snake, for instance — may branch 

 into two, or in others be double from its origin," is somewhat misleading, since it 

 implies that in this snake there are two common carotid arteries. One of the 

 most interesting points in the arterial system of the grass-snake, however, is 

 the fact that as the right common carotid is reduced during embryonic develop- 

 ment to a very small twig which supplies only the thyroid gland, the whole of the 

 blood-supply to the head is carried by the left common carotid. Three special 

 arterial anastomoses are developed in order to allow the blood to be conveyed 

 to the right side of the head. 



The key to the identification of the various species by means of their external 

 characters and the list of the species found in the different regions of Europe are 

 very handy. Although it is stated on p. 135 that the vipers are the only very 

 dangerous snakes, this information would be more easily referred to if the 

 individual species in either of the above lists had been marked according to 

 whether they were slightly, considerably, or not at all poisonous. 



The systematic part contains a full yet concise description of all the snakes 

 found in Europe, together with an account of their distribution, local varieties, 

 and habits. This is indeed very useful for reference, and its value is greatly 

 enhanced by the completeness of its illustrations, mostly from the very accurate 

 drawings by Prof. Sordelli of Naples. 



The few criticisms offered above do not alter the fact that the volume is a very 



desirable addition to our knowledge. It is certainly a work that should find 



a place on the bookshelf not only of the naturalist, who will learn much from its 



well-filled pages, but also of the general reader who wishes to know something of 



the general characteristics of snakes or the particular forms to be found in Europe 



from one who has command of a facile pen and a remarkable knowledge of his 



subject. 



C. H. O'D. 



Les Zoocecidees des Plantes d'Europe et du Bassin de la Mediterranee. 



Tome 3: Supplement 1909-12. By C. Houard. [Pp. 312. With 1567 

 figures and 8 portraits.] (Paris : A. Hermann et Fils, 191 3. Price 10 

 francs.) 

 The vast majority of the parasites which attack plants are either fungi or 

 insects, and the result of the attack is either (1) a drain on the food-resources of 

 the host, which if severe may so weaken it that it succumbs to adverse conditions 

 otherwise easily overcome, or (2) the production of injurious substances which 

 cause local or even general death, or (3) a stimulus to local growth. As regards 

 (1) and (2) it may be said that general death as the result of parasitic attack is a 

 rare occurrence in the higher plants, only taking place when the parasite blocks 

 up the wood vessels, thus cutting off the water-supply to the leaves, or invades 

 the whole plant. In most cases, death is likely to be merely local, since plants 

 present a striking contrast with animals in the fact that they have no means for 

 the rapid distribution of poisons locally produced nor any regulatory centres whose 

 injury upsets the entire system. 



The location of a parasite in a plant is often marked by deformities which 

 frequently appear as circumscribed swellings, or galls, and are usually conspicuous 

 structures of peculiar and fantastic or beautiful form, especially in the case of 

 animal-induced galls (zoocecidia). The chief animal gall-producers, apart from 

 the nematodes (eelworms) whose attention is usually confined to the roots of 



