1894.] the Life-History of the Foraminifera. 159 



While the megalospheric form is not found in process of transition 

 into the microspheric, it is found, either with the protoplasm broken 

 up into swarm cells (Polystomella), or containing megalospheric 

 young in the peripheral chambers, while the central chambers are 

 empty (Orbitolites) . In both cases the megalosphere remained un- 

 absorbed at the centre of the shell. 



The microspheric form is found in the young condition. 



The nuclear characters of the two forms are, at any rate, in the 

 species which I have examined, quite distinct. 



It appears then that it may safely be concluded that the microspheric 

 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 represent different sexes, or they are members of 

 a recurring cycle of 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, both megalospheric and microspheric forms are found 

 with the young of the megalospheric form (primitive discs) in their 

 brood chambers. Other genera furnish analogous, though less com- 

 plete evidence. Hence it is impossible to regard either form as 

 male. 



We turn then to the other hypothesis that the two forms are 

 members of a recurring cycle of generations. On this view it is 

 necessary to suppose, from the evidence afforded by Orbitolites com- 

 planata, in which both microspheric and megalospheric forms have 

 been found with the young of the megalospheric form in their 

 brood chambers, that the megalospheric form may, at any rate in 

 some genera, be repeated for one or more generations, before the 

 microspheric form recurs. No evidence of such a repetition has, 

 however, been furnished by the examination of Polystomella. 



The view that the life-history of the Foraminifera comprises more 

 than one generation is in harmony with the fact that the nuclear 

 history of the two forms in Polystomella, so far as it has been ob- 

 served, presents resemblances to that which Brandt has recently 

 described in Thalassicola amo'ng the Badiolaria. In this group, as is 

 well known, the individuals of a species fall into two sets, those pro- 

 ducing isospores and those producing anisospores, which are regarded 

 as an asexual generation alternating with a sexual. 



The simultaneous division of nuclei by karyokinesis immediately 

 before the formation of the reproductive elements which was ob- 

 served in the megalospheric form of Polystomella is a phenomenon of 

 very general occurrence. A similar division has been shown to occur 



