ON THE LIFE-HISTORY OF THE FORAMINIFERA. 109 



If such a process were to occur, the replacement of the 

 chambers would not take place very rapidly, and various stages 

 should be found. Such stages are, however, not found. 



While the megalospheric form is not found in process of 

 transition into the microspheric, it has been found either with 

 the protoplasm broken up into zoospores {Polystomella), or con- 

 taining megalospheric young in the peripheral chambers, while 

 the central chambers are empty (Orbitolites, &c.). In both 

 cases the megalosphere remains unabsorbed at the centre of the 

 shell. 



The microspheric form is met with in the young stage (fig. 7), 

 though such specimens are necessarily rare, owing to the small 

 numbers of the microspheric form as compared with the megalo- 

 spheric. 



The nuclear characters of the two forms are, in the species at 

 any rate which I have examined, quite distinct. 



It appears that we may safely conclude that the micro- 

 spheric and megalospheric forms are distinct from their origin. 



What then is their relationship ? 



When two forms of a species are met with in animals or 

 plants they generally either belong to different sexes or they 

 •are members of a cycle of recurring generations. 



The hypothesis that the two forms of the Foraminifera 

 represent the two sexes appears to be disproved by the fact that 

 in Orbitolites complanata, Lamk., both megalospheric and micro- 

 spheric forms are found with the young of the megalospheric 

 form (primitive discs) in their brood chambers. Other genera 

 "furnish analogous, though less complete evidence. Hence it is 

 impossible to regard either form as male. 



We turn then to the other hypothesis, namely, that the two 

 forms are members of a recurring cycle of generations. 



[This view receives further support from the facts that in 

 the reproduction of the microspheric form (Postscript 2) the 

 whole of the protoplasm of the parent is divided into the 

 young, and that these all belong to one form, the megalo- 



