REVIEWS 175 



with in junior courses in this country, but does not reach the standard that is 

 generally expected from senior students. In order to avoid the possibility of the 

 student copying figures instead of drawing them from his own preparations, the 

 plan of introducing species other than those dissected is adopted. The end 

 aimed at is a laudable one, but we do not like this way of attaining it, for there is 

 always the possibility of misinterpretation. It is better for the teacher to see that 

 the student does not merely reproduce text figures than to do as is done here in 

 certain cases, e.g., to provide a diagram of a cockchafer for a dissection of 

 a locust, not merely a different species but a different order of insect. Most of the 

 figures are reproductions from other text-books — a matter for regret since those 

 from original papers, e.g., 21, 22, 47, and 49 are very useful, while the two original 

 diagrams, namely 32 and 38, are excellent models of what text-figures in a practical 

 book should be. They are clear, more or less generalised, and instructive. The 

 descriptions and directions are throughout easily followed, although certain 

 misprints have crept in, e.g., Bentam for Benham, fig. 20, Dalage for Delage, 

 fig. 5, and Anadonta for Anodonta, fig. 43. Although perhaps useful in the 

 Unitedi States, it is not likely to be employed generally in this country, where 

 the types are not available, but only for occasional reference. 



C. H. O'D. 



Growth in Length: Embryological Essays. By Richard Assheton, M.A., 

 Sc.D., F.R.S. [Pp. xi + 104, with 42 illustrations.] (Cambridge : at the 

 University Press, 1916. Price is. 6d. net.) 



This interesting little book is composed of two parts. The first is a series of three 

 lectures on "The Growth in Length of the Vertebrate Embryo," originally 

 delivered to the University of London, and the second is the reprint of an article 

 on the Mechanics of Gastrulation from the Archiv fiir Entwicklungs?nechanik 

 der Organismem. Both these are cognate subjects to which the author devoted 

 many years of thought, and so the book forms a fitting memorial to one whose 

 early death has left a noticeable gap in the ranks of the embryologists in this 

 country. The author himself intended to publish the lectures, but the actual work 

 of arranging them for the press devolved on his widow. The subject-matter of the 

 lectures was doubtless left mainly in the form of notes, and one feels that in certain 

 places a little more explanation, doubtless supplied en fiassa?it in the lectures when 

 delivered, would have rendered them more easily followed by the general zoologist 

 not possessing considerable knowledge of vertebrate embryology. 



Apart from this point, which makes difficult reading here and there, the lectures 

 are extremely interesting. It is not possible in the limits of a short review to do 

 justice to the theories so cogently put forward, for the lectures themselves are the 

 summaries of much original work and thought. If the main thesis of the rela- 

 tions of the long axis of the vertebrate to the plane of the ccelenterate mouth be 

 established, it throws considerable light on the origin of the Vertebrata. It will be 

 necessary to go a long way back in the animal kingdom in order to find any 

 representative of the ancestral stock of the vertebrates. It will also be necessary 

 to consider it when dealing with questions of metameric segmentation. Whether 

 the theories be finally accepted or not they are presented in such a thoughtful way 

 and accompanied by such evidence that they will have to be well considered by all 

 future workers. More than this, we feel sure that the hope expressed in the intro- 

 duction will be realised, and the publication of this volume will " inspire others to 

 delve into this . . . fascinating field of research." Beside the general interest of the 



