1907.] on the Foraminifera. 498 



beginniii2^ of the movement they are dispersed over a wide area, and 

 each l)ecoiiies the centre of a system of a pseudopodia of its own. 



The whole of the protoplasm of the parent is nsed up in the 

 formation of the brood of young, the shell beino: left empty. The 

 process, from the first appearence of the halo to the dispersal of the 

 young, is complete in about twelve hours. 



In a short time the protoplasm which lies outside the aperture of 

 each of the spheres secretes the Avail of a second chamber of charac- 

 teristic shape, and the young individual is then clearly recognisable 

 in size and shape as the tw^o-chambered young of the megalospheric 

 form. Each of the spheres was, in fact, a megalosphere. The 

 microspheric parent has given rise to, indeed it has become, a brood 

 of megalospheric young. 



[A series of 12 lantern slides was shown, illustrating the mode of 

 reproduction of the microspheric form, and the dispersal of the 

 megalospheric young. They were taken from a series of photographs 

 of the successive stages of reproduction of one individual.] 



As the young megalospheric form grows and the number of 

 chambers increases, the single nucleus, which originally lay in the 

 megalosphere, moves on through the chambers, becoming constricted 

 as it passes from one to another. It also gives off chromidia into 

 the protoplasm, and eventually as the reproductive phase of the 

 megalospheric form approaches, the nucleus loses its compact shape and 

 staining power, and finally disappears. Hosts of minute chromidia 

 may then be found scattered through the protoplasm. These become 

 aggregated as distinct nuclei, the protoplasm gathers about them, and 

 they divide by karyokinesis. Then follows a second karyokinetic 

 division, and, the protoplasm having divided correspondingly, the 

 whole contents of the megalospheric shell emerges as a multitude of 

 minute biflagellate zoospores some 4 /x in diameter. 



This was the stage which had been reached in the study of the 

 life-history up to about 4 years ago. The formation of the zoospores 

 had been observed, but the fate which befell them remained a matter 

 of inference. 



The evidence pointed strongly in the direction of the view that 

 the foraminiferal life-history consists of an alternation of generations. 

 While the megalospheric form would, on this hypothesis, arise by a 

 simple vegetative asexual reproduction of the microspheric parent, 

 many considerations seemed to indicate the probability that the 

 microsphere, the initial chamber of the microspheric form, arose by 

 the conjugation of zoospores. In addition to the general probability 

 of the occurrence of a sexual stage somewhere in the life-history, the 

 sizes of zoospore and micros]3here fitted in with the view that the 

 latter might be formed by the coalescence of two of the former. 

 Again, the fact of the rarity of the microspheric form in comparison 

 with the megalospheric was comprehensible, on the supposition that, 

 to be able to conjugate, the zoospores must be of different parentage. 



