Heron- A I, LEV and FvAki.ani) — Hliuhi of Ycrncuilinn pohjslropha. \-')7 



generally accepted naine of (liniorjiliisin, has deeply interested students of the 

 l)iiinoniies ol' tlie Fnraiiiiiiii'era ever since it was established Ky MiiniiT- 

 Clialinas in 1880 in the Numniulites.' Since that date the phenomenon lias 

 been established in a great many Foraminifera. Few authors have devoted 

 more attention or eonlributed more to our knowledge of this phenomenon 

 liian -I.J. Lister." The subject is too invol\ed to claim more than a passing 

 reference in this place, especially as we are still in ignorance as to its influence 

 or conuexion if any, with the problems under discussion. 



(ii) The second form of variation, viz., the adoption by a Foraniinifer, at 

 consecutive stages of its existence, of different plans of growth, has been 

 recognized ever since the study of the Foraminifera had its inception, and was 

 originally known as dimorphism and trimorphism. As early as 1826 a sub- 

 genus e.xhibiting this phenomenon was named Dimorphina by d'Orbigny.'" 

 But since Munier-Chalmas' discovery of the dimorphism of the primordial 

 chamber the older sense of the word has been generally abandoned, and the term 

 " dimorphism" has been restricted to his definition. Various substituted terms 

 have been suggested for the earlier discovery. Chapman in 1898 suggested 

 bigenerism,^'^ which was not happy, in view of the fact that such variations 

 sometimes include more than two generic plans of growth. Moreover, a genus 

 presenting tliis feature had been named Bigenerina in 1826 by d'Orbigny." 

 Ehumbler in 1895 suggested using the adjectives '• bi-formed " or " tri-formed " 

 to describe this kind of variation ;^^ but Lister may be said to have established 

 a more convenient term in the word " multiformity," i' and this term we have 

 adopted. 



This is neither the time nor the place to deal with the lengthy arguments 

 as to whether multiform shells are progressive or retrogressive in their plans 

 of growth. Probably in most cases the change of plan during the growth of 

 the shell marks a progression or evolution to a higher and more complex 

 system, and in such cases the complete shell may exhibit its full ancestry in 



' E. C. P. A. Munier-Chalmas: " Sur le Dimorphisme des Nummulites." Bull. Soc. 

 Geol. France, Ser. 3, vol. viii, p. 300. 



" See especially, J. J. Lister, "Contributions to the Life History of the Foraminifera," 

 Phil. Trans. Roy. Soc, vol. clxxxvi (1898), B, pp. 401, et sei/., and loc. cit. (note 5), pp. 59, 

 et passim. 



'" A. d'Orbigay : •' Tableau Methodique de la Classe des Cdphalopodes." Ann. Sci. 

 Nat., vol. vii, 1826, p. 264. 



" F. Ch-vpman : " P'oraminifera of theGault of Folkestone." J. R. Micr. Soc, 1898. 

 p. 14 (foot-note). 



^- Loc. cit. (note 10), p. 261. 



" L. Rhumbler : " Entwurf eines natiirlicheu Systems der TliaUuu)i>lioren." Xachr. 

 d. k. Ges. d. VViss. zu Gottiugen, 1895. iMath. pliys. Kl., Pt. 1, p. 03. 



'■* Loc. cit. (note o), p. 58. 



