RECENT ADVANCES IN SCIENCE 59 



(Ann. and Mag. Hist. Hist. Nov. 191 7) ; "A Hermaphrodite 

 Dogfish," by Bamber (Proc. Zool. Soc. Nov. 191 7) ; " On the 

 Herring in Captivity and on an Effect of the Environment on 

 the Structure of this Fish," by Williamson (Journ. Zool. Re- 

 search, Nov. 191 7) ; "Sinneslinen und freie Nervenhiigel bei 

 Chimcera monstrosa," by Ruud (Zoolog. Jahrb. 191 7) ; " De- 

 scriptions of new Frogs of the Genus Rana," by Boulenger 

 (Ann. and Mag. Nat. Hist. Dec. 191 7) ; and " On the Skull 

 of Tritilodon longcevus, Owen," by Petronievics (ibid. Oct. 

 1917). 



Two papers deal with the primordial cranium, viz. " The 

 Primordial Cranium of Microtus amphibius (Water-Rat) as 

 Determined by Sections and a Model of the 25 mm. stage, with 

 Comparative Remarks," by Fawcett (Journ. of Anat. July 

 191 7), and " The Primordial Cranium of the Cat " by Terry 

 (Journ. of Morph. vol. xxix. Sept. 191 7). It is not possible 

 to summarise these papers as their value lies in the accuracy 

 and minuteness with which the primordial cranium is described. 

 The excellent illustration of the model renders it an easy matter 

 to follow the description. Although still in an early stage of 

 development, a fair amount of ossification had already set in 

 in some of the cartilages. The work of the second is in the 

 main based upon the wax-plate model of the chondrocranium 

 of an embryo of 23*1 mm., but a number of other stages have 

 been utilised. The two researches add considerably to our 

 knowledge of the mammalian cranium. 



In " The Cytomorphosis of the Marsupial Enamel Organ 

 and its Significance in Relation to the Structure of the Com- 

 pleted Enamel," by Carter (Phil. Trans. Roy. Soc. B, vol. 

 ccviii. Dec. 191 7), we have for the first time the description 

 of the enamel organ and completed enamel studied by satis- 

 factory modern histological methods upon well-fixed material. 

 Only too often in odontological work does the fixation and 

 technique leave much to be desired. Marsupial teeth differ 

 from those of most mammals in the presence in the enamel of 

 structures, presumably organic, passing sinuously outwards 

 from the dentinal tubules with which they are continuous. 

 These " fibrils " arise from " the coagulation or gel-formation 

 of an organic substance not usually present in colloidal secretion 

 shed by the enamel cells." Their development is associated 

 with distinct changes in the ameloblasts which elongate and 



