THE FORAMINIFERA 



more direct communication with the outer, and so with the 

 exterior. 



Reproductive Phase of the Megalospheric Form. In specimens in 

 which the large nucleus has disappeared hosts of minute nuclei 

 may be found, scattered uniformly or in groups through the 

 protoplasm. 



Presumably these are derived from constituents of the principal 

 nucleus, and possibly of the small nuclear fragments as well, but 

 their precise relation to these bodies has not been followed. 



When the nuclei are evenly distributed the protoplasm breaks 

 up into minute rounded masses, the centre of each being occupied 

 by a nucleus. Division of these nuclei by karyokinesis now occurs, 

 and is simultaneous or nearly so throughout the organism, and 

 this is followed by a second division of the protoplasm to form 

 rounded bodies about 3-4 /x in diameter, each containing one of the 

 daughter nuclei (Fig. 12). At a later period the contents of the 



shell issue as active zoospores 

 of approximately uniform size, 

 which swim rapidly by means of 

 flagella. 



It is to be noted that, as in 

 the case of the reproduction of 

 the microspheric form, the whole 

 of the protoplasm of the parent 

 is used up in the production of 

 the zoospores. 



Though the zoospores have 

 been seen issuing from the 

 shell, their precise characters, 

 when ripe, have not been accur- 

 ately described ; nor have we as 

 yet direct evidence as to their 

 fate. 



That there is a close relation 

 between the zoospore and the 

 microsphere is suggested by the fact that there is no great differ- 

 ence in size between these structures, the diameter of the former, 

 before their escape from the parent shell, being 3-4 /A, and that of 

 the latter about 10 /A. A further piece of evidence tending in 

 this direction is furnished by an observation of Schaudinn's (44, 

 p. 92). In an aquarium containing abundant Polystomellas, 

 Schaudinn suspended coverslips by means of threads, so arranged 

 that the lower borders of the coverslips were separated by about 

 2 cm. from the stratum covering the bottom of the aquarium. 

 After two days young examples of the microspheric form were 

 found on the coverslips. Now throughout the vegetative phases 



Fio. 12. 



Section through a specimen of the niegalo- 

 spheric form of Polystomella crispa, in which the 

 contents are divided up into zoospores. x 160. 



