Dimorphism of the Foraminifera. 341 



Society of France in January 1881 (Bull. Soc. G&)1. France, 

 s£r. 3, tome ix. p. 171), in which, after discussing the pheno- 

 mena observed by him and indicating the pairs of so-called 

 species of Nummulites which he also recognized, he summed 

 up his opinions as follows (L c. p. 1 75) : 



u If the species of the same couple have some common 

 characters, such as analogous external adornments and septa 

 of the same form and of the same inclination, they have on 

 the other hand plenty of different characters, such as — spiral 

 of which the mode and rate of coiling is different, septa 

 differently spaced and distributed, especially in the vicinity of 

 the centre, and chambers diffeiing in form, size, and number. 



u r v 



lo pass from one form to the other, therefore, we have not 

 merely to prolong the spiral, but to modify it in its essential 

 elements. The internal arrangement of the two forms has 

 been made in accordance with two plans of architecture which 

 are completely different, and of which it is impossible to derive 

 the one from the other. 



" Ah ! had ftf . Munier-Chalmas expressed the opinion that 

 these two similar forms are the two sexes of the same species, 

 it would have been more difficult to answer him, so much do 

 the circumstances of their constant association, their relative 

 frequency, and the analogy of their external characters give 

 them the air of a veritable couple. No doubt it will be 

 answered that there is nothing in the organization of the 

 existing Rhizopods to justify one in supposing that there is 

 any separation of sexes in them. But is this answer conclu- 

 sive ? Evidently not. 



" Our conclusion therefore is that in each couple of Num- 

 mulites there are such anatomical differences between the two 

 forms with and without a central chamber that it is impossible 

 to consider them two ages of the same species. It would be 

 more probable to regard them as the two sexes, if our actual 

 knowledge with regard to the physiology of the Rhizopoda 



was not opposed to this view." 



Remarks upon the subject of the occurrence of pairs of 

 Nummulites as described by M. De la Ilarpe, and on the 

 presence in them of large and small primordial chambers, will 

 be found in various parts of the ' Catalogue of the Fossil 

 Foraminifera in the Collection of the British Museum,' by 

 Prof. T. Rupert Jones (1882), the supplementary notes to 

 which also contain the translation of a letter from M. De la 

 Harpe to the author relating to the same subject. 



