294 SCIENCE PROGRESS 



Broom (Proc. Zool. Soc. May 1916). Certain bones are de- 

 scribed which are possibly the homologues of the tabular of 

 the Therapsid reptiles, and also of the reptilian surangular. 

 At the same meeting Woodward read a paper on the ramus of 

 a marsupial mandible from Alberta, Canada. It obviously 

 belonged to an opossum-like animal, and is termed Cimolestes 

 cutleri. The old theory that the chin is developed in relation 

 to articulation is rejected by Waterman in the " Evolution of 

 the Chin " (Amer. Nat. April 191 6), who regards it as due to the 

 reduction of a once large lower jaw. By means of the recon- 

 struction method, Esdaile has carried out an investigation 

 " On the Structure and Development of the Skull and Laryn- 

 geal Cartilages of Perameles, with notes on the Cranial Nerves " 

 (Phil. Trans. Roy. Soc. vol. ccvii. B). This contains also a 

 comparison with the skulls of Cynodonts, Prototheria, Tricho- 

 surus, Dasyurus and the higher mammals. 



General. — " An Experimental Determination of the Factors 

 which cause Patterns to appear conspicuous in Nature " was 

 conducted by Mottram (Proc. Zool. Soc. May 191 6). The most 

 conspicuous object was found to be a circular disc of black 

 with a white centre. The remaining papers occur in the 

 American Naturalist, so that it will only be necessary to give 

 the month of publication. Muller has a series of three papers 

 on " The Mechanism of Crossing Over " (Part I. April ; Part II. 

 May ; and Part III. June 1916), the concluding part of which is 

 still to come. As is now well known, the study of a large number 

 of factors in the same animal has shown that these characters 

 run in series, a phenomenon known as linkage. However, if 

 a sufficient number of such linked series be taken it will be 

 found that a certain group of one series changes over with a 

 group from another series, this being termed crossing over. 

 The object of these papers is to review the outstanding evidence 

 relating to this phenomenon, and to describe a new experi- 

 mental method of studying such separation. The results of 

 the experiments give a demonstration of the fact that the factors 

 behave as though they are joined in a chain. When interchange 

 takes place, the factors keep together in sections, according 

 to their place in line, and are not interchanged singly. By 

 means of mazes, Bagg has investigated " Individual Differences 

 and Family Resemblances in Animal Behaviour " (April 191 6). 

 It is found that there is a marked difference in individual 



