1899] SUPPOSED MESOZOIC MAMMALS 269 



differentiated there in the midst of the Mesozoic fauna; but whatever 

 be the geological result of these discoveries, we await Dr. Eoth's 

 completed memoir with the greatest interest. 



A Fine Taste in Binding. 



In Mr. Thomson's review of Professor Ewart's " Penycuik Experiments " 

 (Natural Science, xiv. pp. 203-212) no notice was taken of a feature 

 which should not have escaped a naturalist's eye, we mean the 

 "external characters." It is with these that a biological description 

 should begin, and in this case they are striking enough. We believe 

 that the quaint work called The Evergreen, also an Edinburgh product, 

 had its spring number at least clothed in lamb's skin, which was 

 suggestive enough of the gentle bleatings within. It is strange 

 therefore that one of the authors of The Evergreen should have failed 

 to remark that " The Penycuik Experiments " are clothed " in zebra." 

 We would congratulate the author and the publishers on this elegant 

 binding in the hope that others will follow their example. How much 

 it would add to the grace of our bookshelves, how much it would 

 lessen the labour of finding a book, if each volume were so to speak 

 indexed by its binding. How ineffably better than any decimal 

 notation if biologists would in their binding rehabilitate the " doctrine 

 of signatures." We read that " Matopo " became strangely excited 

 when he saw a zebra skin ; we should like to know what he did when 

 he saw the book. 



The True Function of the Thymus. 



Dr. John Beard is to be congratulated on having arrived at the 

 solution of a problem which he has had before him for years, — the 

 function of the thymus. Since Kolliker discovered its origin in 

 mammals from the epithelium of a gill -pouch, and stated that the 

 original epithelial cells gave rise to lymph cells or leucocytes, two 

 views have been held regarding- this puzzling organ. " On the one 

 hand, Stieda and His have maintained that the leucocytes which 

 always form integral parts of the thymus soon after its first origin 

 have migrated thither from the exterior, possibly from the mesoblast. 

 In this conclusion they have been supported by the researches of 

 Dohrn, Gulland, and Maurer, and by almost every text -book of 

 embryology and comparative anatomy published since 1879. On the 

 other hand, Kolliker has stoutly maintained his original position, and 

 the results of his investigations have been emphatically confirmed by 

 Prenant, Oscar Schultze, and Beard." So far the historical aspect. 

 But Beard has now shown {Lancet, January 21, 1899) that in the 



