108 J. J. LISTER. 



Contributions to the Life-History of the 

 Foraminifera. 



By 

 J. J. Lister^ IVI.A. 



with plates v.— viu. 



Introduction. 



In the preface to his classical work, 'Uber den Organismus 

 der Polythalamien/ published in 1854, Max Schultze acknow- 

 ledged with regi-et the incompleteness of the account which he 

 was able to give of the reproductive processes of the Foramini- 

 fera, and pointed out that a rich field here lay open for future 

 investigation. 



In the years that followed Schultze himself made further 

 contributions to our knowledge on this head, but, important as 

 they were, they only went a short way towards solving the 

 pi'oblem. 



Of late Munier-Chalmas and Schlumberger have con- 

 tributed an essential factor in demonstrating the existence of 

 dimorphism in many and widely separated species of Foramini- 

 fera. It has been shown in many cases that the individuals of 

 a species fall into two distinct sets. In one, the first formed 

 chamber is very minute, while in the other it is large. Differ- 

 ences in the size attained by the adult shell, in the plan of 

 symmetry on which the chambers are arranged, and, as I have 

 to show, in the nuclei may also be present. Munier-Chalmas 

 and Schlumberger distinguish the two groups as Form A, 

 with a viegasj^here, and Form B, with a micros2)here. I have 

 ventured to modify one of these terms, and refer to the forms as 



