NOTICES OP NEW BOOKS. 319 



in large flocks at the approach of winter, and that the northern 

 limit of its winter range takes in the southern counties of 

 England. 



We are informed by the Preface that it is proposed to publish 

 as a continuation of this work, and uniform with it, Illustrations 

 of all the species of Passerine birds which are migrants to the 

 British Islands, omitting the occasional visitors, and in a subse- 

 quent volume the resident and migratory Picarice. This will be 

 an expensive undertaking, but we trust, for the sake of the 

 enthusiastic author, that the list of subscribers' names (which 

 are received by Messrs. Wesley & Son) may be sufficiently long 

 to justify him in carrying out his intention. 



Alternating Generations : a Biological Study of Oak-galls and 

 Gall-flies. By Hermann Adler, M.D. Translated and 

 edited by Charles B. Straton. Post 8vo, pp. i — xliii; 

 1 — 198. With Coloured Plates and other Illustrations. 

 Oxford : Clarendon Press. 1894. 



In an excellent Introduction of forty pages, with which Mr. 

 Straton paves the way for his translation of Dr. Adler' s essay, 

 he gives not only a clear review of the chief literature on the 

 subject of galls, but an instructive resume of the different views 

 which have been expressed by eminent naturalists as to the 

 cause or causes of their formation. Darwin, and many writers 

 before him, held that gall-formation was due to a chemical 

 secretion injected by the gall-insect; Malpighi considered that 

 it acted as a ferment on juices existing in the plant ; and this 

 was the view of Beaumur, but he added to it the thermal effect 

 of the egg, and the nature and character of the wound, which 

 varies according to the shape of the ovipositor of each species. 

 Dr. Derham thought the formation was partly due to the act of 

 the plant, and partly to some virulency in the juice, or egg, or 

 both, reposited on the vegetable by the parent animal, and just 

 as this virulency is various according to the difference of its 

 animal, so is the form and texture of the gall excited thereby. 



Darwin speaks of galls as produced by a minute atom of the 

 poison of a gall-insect, and compares them to the specific local 

 processes of zymotic diseases. Sir James Paget, in 1880, 



