THE FORAMINIFERA 75 



arise from eggs which are, so far as observation has yet advanced, 

 similar, and are most differentiated when adult. (2) Although 

 the differentiation of male and female gametes is known in several 

 groups of the Protozoa (Sporozoa, Ciliata, Flagellata), a differentia- 

 tion of the parent organisms which produce the gametes, which 

 would be the phenomenon comparable with the sexual dimorphism 

 of the Metazoa, is unknown among the Protozoa. 



But apart from a priori objections, it may be well to try how 

 the ascertained facts of the life-history fit this hypothesis. The 

 megalospheric form, producing zoospores, would evidently on this 

 view represent the male, while the microspheric form, producing 

 the large megalospheres, might be regarded as the female. It 

 might be supposed, the fate of the zoospores being unknown, that 

 they unite with and fertilise the megalospheres. But while the 

 origin of the megalospheric form, the supposed male, is thus 

 accounted for, that of the microspheric form, the supposed female, 

 remains unexplained, and as the whole of the protoplasm of the 

 parent is, to all appearance, used up in the brood of megalospheric 

 young, the hypothesis is at fault. Moreover, in Orbitolites, 

 Cornuspira, and other genera the megalospheric form may also give 

 rise to a brood of megalospheric young, a proceeding foreign to 

 the nature of a male organism. Hence neither of the forms of the 

 species conforms to the character assigned to it by the hypothesis : 

 the microspheric form, the supposed female, in that it does not 

 produce " females " ; the megalospheric form, the supposed male, in 

 that it does in some instances produce " males." 



A third hypothesis is in harmony with what we know in other 

 groups of the Protozoa, and fits the ascertained facts. It is that 

 the two forms represent alternating or recurring generations in a 

 life-cycle. The individuals of the microspheric form reproduce 

 asexually by the multiple fission of their protoplasm to form broods 

 of megalospheric young. The individuals of the megalospheric 

 form may undergo, in some genera, a similar process, but ulti- 

 mately a megalospheric individual is produced whose protoplasm 

 divides into zoospores. 



How is the gap between the zoospore and the microsphere 

 filled 1 



That they are closely related is suggested, as stated above, by 

 their approximation in size, and by the indication, afforded by the 

 colonisation of Schaudinn's coverslips, of a free swimming stage 

 preceding the vegetative phase of the microspheric form. Another 

 remarkable fact bearing on the matter is the scarcity of the micro- 

 spheric form in comparison with the megalospheric, a scarcity all 

 the more striking when it is borne in mind how far more numerous 

 are the zoospores produced by one megalospheric individual than 

 the members of a brood of megalospheres. 



