113 



Schlumberger, and by their united efforts the existence of a 

 dimorphic origin has been demonstrated in the case of over twenty 



The question that immediately arose, and awaited solution, 

 was, " What is the meaning of this dimorphism ?" That it had a 

 distinct relationship to the process of reproduction was generally 

 inferred, and its significance in this respect has given rise to 

 much discussion. The first point that required determination 

 was whether the dimorphic features were aboriginal in the history 

 of the individual, or caused subsequently to birth by a secondary 

 growth of smaller chambers within the macrospheric chamber, an 

 alternative that was soon decided in favour of the view that the 

 difference was aboriginal. 



In 1894 Mr. J. J. Lister, in a paper read before the Royal 

 Society of London on " The Life History of the Foraminifera," 

 gave a full and lucid resume of the state of knowledge on this 

 subject to date, with many valuable, original observations. 

 Lister's researches have been directed chiefly to the study of the 

 nuclei of Foraminifera in relation to reproduction. His observa- 

 tions were confined to a limited number of forms, and chiefly 

 the cosmopolitan species, Polystomella crispa. This careful 

 observer was able to note that the nuclei of the megalospheric 

 and microspheric individuals of a species differed essentially from 

 each other. The megalospheric form carries but one large 

 nucleus during the greater part of the life of the individual, 

 whilst the microspheric form, in the place of a large central 

 nucleus, contains several small nuclei. This discovery of a 

 physiological, as well as a morphological difference, in the two 

 forms strengthened the assumption that they owed their difference 

 of form to aboriginal causes. 



The next point was to establish what relationship the two 

 forms bore to each other in the life history of the species. Did 

 the difference of form mark a difference of sex ? Or did the two 

 forms represent a cycle of recurring generations, as may be seen 

 in some other departments of Natural History 1 Lister was led 

 to discard the sexual hypothesis chiefly from the study of Orbito 

 lites complanata, in which he found the young of the megalo- 

 spheric form in the brood chambers of both megalospheric and 

 microspheric individuals; "hence," he says, "it is impossible 

 to regard either form as male." In a postscript to his paper, of 

 slightly later date, he reaches a definite conclusion on this point 

 in the following words, " The fact that the whole of the proto- 

 plasm of the parent is used in the production of the young, and 

 that these are all of one form, supports the view that the two 

 forms of the Foraminifera belong to different generations."* 



* Op. cit., p. 446. 



