LINNEAN SOCIETV OF LONDON. 77 



■within the Dicotyledons, from llie generalized types among the 

 Eanales to the most highly differentiated Sympetak?, one of the 

 chief underlying principles seems throughout to be the reduction 

 of parts*. 



With current Mendelian conce|)tions the 'Law of Loss' har- 

 monises without apparent ditllculty. If evolution — at least in 

 what Dr. Guppyt would distinguish as the later "differentiating" 

 or "adaptive" stages — lias proceeded by variations due to suc- 

 cessive losses of factors, we should certainly expect that the 

 complete loss of au organ might be associated witli inability to 

 recall it, even when circumstances seem to put a premium upon 

 its reappearance. t 



List of Memoirs cU'-d. 



Arber. a. (1918.) The Phyllode Theory of the Monocotyledonous 



Leaf, witli special reference to anatomical evidence. Ann. Bot. 



vol. xxxii. 1918, pp. 465-501, 32 textfigs. 

 Caxdolle, A, F. DE. (1827.) Organograpbie vegetale. Vol. i. I'aris, 



1827. 

 Case, E. C. (1897.) On the Osteology 'i-iid Relationships of Frotosiega. 



Journ. Morph. vol. xiv. 1897, pp. 21-55, 3 pis. 



Celakovskv, L. J. (1894.) Das Reductionsgesetz der Bliithen. Sitz. 



d. k. Eiihm. Gesellsch. der Wiss., math.-nat. Classe, Jahrg. 1894. 



(Pubh shed 1895.) 142 pp. 

 Chuuch, A. II. (1908.) Tvpes of Floral Mechanism. Parti. Types 



i.-xii. Oxford, 1908.' 

 Dbp^eet. L\ (1907.) Les Transformations dii Monde Animal. Paris, 



1907. 

 DoLLO, L. (1893.) Les Lois de TEvoliition. liull. de la Soc. Beige de 



Geol. de Pnleoiit. et de Hydrol. T. 7, 1893 Proces-verbaux. 



Seance du 25 juillet, 1893, pp. 164-16(1. 

 Doi.LO, L. (1899.) Les ancetres des Marsupiaux etaient-ils arboricoles ? 



Travaux de la Station Zool. de Wimereux. T. 7, 1899. pp. 188- 



203, 2 pis. 

 DoLLO, L. (1901.) Sur I'origine de la Tortue Luth {Dermochelys cori- 



acea). Bull, de la Soc. roy. des sci. nied. et nat. do Bruxelles, 4 fev. 



1901,v(d. lix. pp. 28-51. 



* It is perhaps scarcely necessary to quote authorities for this statement, but 

 ■we may refer in passing to the "reduction-specialisation" recognised by Church 

 (1908) in his study both of the vegetative and reproductive organs of flower- 

 ing plants ; tiie tendency to economy of ]«irts repealedly emphasized by 



Wernham (1911 and 1912) ; and llie reduction postulated by Celakovsliy in ;i 

 ■well-known niemoir (1894). 



t Guppy, H. E. (1919). 



\ Since this ]:)aper was read before the Linnean Society, Prof. B. Petronievics 

 has published a full analysis and critical study of all that part of Dollo's work 

 whicli relates to the Law of Irreversibility ("Sur la Loi de I'Evolution Irre- 

 versible," Sci. Prog. vol. xiii. 1919, pp. 40C-419). The Zoological Secretary 

 lias also kindly called my attention to a paper by I). Keilin in support of 

 Dollo's Law (" La loi d'irrcversibilite de I'evolution (DoUo), vcrifiee par 

 I'etude des larves d'insectes," Bull, de la Sue. Zool. de France, \ol. xi. 

 1915, pp. 38-43. For further coTisideralions relating to the Law of Loss, 

 see Arber, A. " On Atavism and the Law of Irreversibility," Amcr. Journ. Sci. 

 vol. xlviii. pp. 27-32, 1919. 



