238 SCIENCE PROGRESS 



main concerned with these forms, a full and useful summary 

 and discussion of other vertebrate types is also given. It 

 is clearly shown that in the pituitary body of the adult, the 

 pars tuberalis is derived from Rathke's pouch, the pars distalis 

 from outgrowths from its walls or the ingrowth of connective 

 tissue into these walls, and the pars neuralis from a hollow 

 outgrowth of the floor of the diencephalon. A remarkable fact 

 came to light, namely that Seessel's pocket forms a part of 

 the hypophysis in Phascolaretos cinereus and Phascolomys 

 Mitchelli, but not in other forms, e.g. Dasyurus, and the 

 significance of this is not yet clear. The characteristic chromo- 

 philic and chromophobic cells are differentiated in situ before 

 the adult condition is reached. 



Other papers include : " On the Skeleton of an Adult 

 Female Small Finner or Piked Whale {Balcenoptera acutoros- 

 trata, Lacepede), " by M'Intosh {Jour. Zool. Research, vol. ii. 

 May 191 7) ; " Some Notes on Three-toed Sloths " (Ann. and 

 Mag. Nat. Hist. April 191 7), " A new Vole from Palestine" 

 (ibid. June 191 7), " On the small Hamsters that have been re- 

 ferred to Criceiulus phceus and Campbelli " (ibid.), all by Thomas ; 

 " The Lemurs of the Hapalemur Group," by Pocock (ibid. 

 April 191 7) ; " Notes on some of the Viscera of an Okapi 

 (Okapia Johnstoni, Lankester)," by Burne (Proc. Zool. Soc. 

 April 3, 191 7). 



General. — Longley contributes " Studies upon the Biolo- 

 gical Significance of Animal Coloration — II. A Revised 

 Working Hypothesis of Mimicry " (Amer. Nat. vol. Ii. April 

 191 7), the first part of which is printed in the Journal of 

 Experimental Zoology and has not yet reached this country. 

 The author criticises at some length the various theories of 

 mimicry, pointing out that most of them are unsatisfactory. 

 It is suggested " that the coloration of typical members of each 

 group is a combination of hues well suited upon the average 

 to render them inconspicuous in such places as they commonly 

 frequent. If this be so, the initial step towards the produc- 

 tion of new cases of mimicry might be any one of many 

 variations in mode of nutrition or reproduction which would 

 lead representatives of the first family to spend their lives 

 after the manner of the second." From this similarity, at first 

 only general, the action of natural selection is all that is required 

 to produce mimics. 



