76 THE FORAMINIFERA 



The analogy of other life -histories would lead us to suppose 

 that at some point in the cycle a sexual process, the conjugation, 

 with nuclear fusion, of two organisms, occurs, and the life-history 

 of Trichosphaerium sieboldi, Schn., which has lately been worked 

 out by Schaudinn (47), to whom so much of the recent advance 

 in our knowledge of the life -history of the Protozoa is due, 

 appears to afford a very appropriate parallel. This form is 

 not included in the Foraminifera, but is a somewhat aberrant 

 member of the allied group the Lobosa. The main features 

 of its life -history are, however, remarkably similar to those of 

 Polystomella. 



The individuals are rounded multinucleated masses of proto- 

 plasm not contained in a definite shell, though surrounded by a 

 gelatinous envelope. They form a dimorphic series, the members 

 of which recur in a cycle of generations. In those of one genera- 

 tion, which may be called by Haeckel's term Amphionts, reproduc- 

 tion occurs by the simultaneous division of the protoplasm about 

 the nuclei to form spherical uninucleated masses, which emerge 

 and grow into the members of the other generation the Mononts. 

 These in their turn break up, after subdivision of their nuclei, into 

 zoospores. The zoospores are biflagellate organisms, and are all 

 alike. 



While the zoospores from the same parent will not unite with 

 one another, those from different parents conjugate readily. In 

 this process, which has been carefully followed by Schaudinn, the 

 nuclei of the two gametes unite, their flagella drop off, and the 

 zygote so produced, absorbing fluid, undergoes a considerable in- 

 crease in size, so that in a few hours its diameter is more than 

 doubled. The zygote shortly afterwards secretes a gelatinous 

 envelope, and the characters of the full-grown individual of the 

 amphiont generation are gradually acquired. The multinucleate 

 condition results from successive mitotic divisions, beginning with 

 that of the nucleus of the zygote. 



In Hyalopus dujardinii, which may be regarded as a member, 

 though an aberrant one, of the Foraminifera, Schaudinn (43) has 

 also observed the conjugation of zoospores, but in this case the 

 process occurred between members of the same brood. 



If we assume that a similar conjugation of zoospores occurs in 

 Polystomella, the facts above alluded to are at once explained. 



The fusion of two zoospores (4 p. in diameter), and the subse- 

 quent expansion of the zygote by the absorption of water before 

 the secretion of a shell, might well form a body of the size of the 

 microsphere (about 1 /*) ; the free locomotive stage prior to the 

 settling down of the microsphere, indicated by Schaudinn's 

 experiment, is supplied ; and the comparative rarity of the micro- 

 spheric form is explained on the supposition that, as in Tricho- 



