300 Mr. J. J. Lister. On the Dimorphism of — [Mar. 2, 
chamber (megalospheric) may arise as the offspring of the form with a small 
central chamber (microspheric) (not “ without central chamber,” as stated by 
de la Harpe), and there are good grounds for concluding (14, pp. 74 to 77) 
that the two supposed “ species ” represent alternating or recurring generations 
in the life history of a single species. This, however, is to anticipate the 
history of the subject. 
To the entirely right conclusion above stated, Munier-Chalmas unfor- 
tunately added an extension of his view which was wrong. It so happened 
that among the microspheric specimens of the species which he investigated 
he failed to find any of so small a size as that commonly attained by the 
megalospheric form; and he concluded that though the two sets of indi- 
viduals constituting a species were in some unexplained way of different 
natures, yet that both began life in the guise of the megalospheric form. At 
a certain stage of growth, it was supposed, the individuals of one, and the 
more abundant set ceased to grow, while the growth of the members of the 
other set proceeded. On the one hand, chambers were added in forward 
continuation of the series already formed, building up the large test of the 
microspheric form; and on the other, at the centre of the test, the large 
central chamber was absorbed, and chambers of smaller and smaller size were 
laid down, continuing the spiral series in a backward direction to the centre. 
In January, 1881, the first part of de la Harpe’s ‘Etude’ appeared, and 
under the head of “ Association of Species” (p. 65) he criticised Munier- 
Chalmas’ conclusions. In the same month, writing in association with de 
Hantken, he addressed a letter to M. Tournouer, of the Geological Society of 
France (6) in which the same criticisms are set forth. 
He had no difficulty in disposing of the second part of Munier-Chalmas’ 
proposition. With regard to the dimorphism of the species of nummulites, he 
says :-—“ Une idée qui, sans avoir été formulée, a cependant traverse l’esprit 
de plusieurs, c’est que ces deux formes sceurs, toujours associées, représen- 
teraient peut-étre les deux sexes de la méme espéce. Rien dans leur mode de 
distribution ni dans leur fréquence relative ne s’opposerait 4 cette hypothese. 
En l’admettant tous les faits deviendraient faciles & comprendre. D’autre 
part, dans les Rhizopodes, non seulement les sexes ne paraissent pas étre 
séparés, mais leurs diverses fonctions ne semblent pas méme localisées. 
Comment done admettre que deux Rhizopodes batis sur des plans différents 
représentent les deux sexes d’une méme espéce ? La question reste donc sans 
solution.’* 
Driven now, as it would appear, by the error of the second part of 
Munier-Chalmas’ proposition, to adopt an attitude very similar to that which, 
* ‘Etude,’ p. 65. 
