FORAMINIFERA 



67 



munications on either type. Ehumbler goes so far as to suggest 

 that all so-called Lagena shells are either the first formed 

 chamber of a Nodosaria which has not yet become polythalamian 

 by the formation of younger ones, or are produced by the separation 

 of an adult Nodosaria into separate chambers. 



Many of the chambered species show a remarkable dimorphism, 

 first noted by Schlumberger, and finally elucidated by J. J. 

 Lister and Schaudinn. It reveals itself in the size of the 



Fig. 15. A, Megalospherlc; B, microspheric shell of Biloculina. c, The initial chamber. 

 The microspheric form begins on the Quinqueloculina type. (From Calkins' Protozoa.) 



initial chamber ; accordingly, the two forms may be distinguished 

 as "microspheric" and " megalospheric " respectively (Fig. 15), 

 the latter being much the commoner. The microspheric form 

 has always a plurality of nuclei, the megalospheric a single one, 

 except at the approach of reproduction. Chromidial masses are, 

 however, present in both forms. The life-history has been fully 

 worked out in Polystomella by Schaudinn, and in great part in 

 Polystomella, Orbitolites, etc., by Lister ; and the same scheme 

 appears to be general in the class, at least where the dimorphism 

 noted occurs. The microspheric form gives birth only to the 

 megalospheric, but the latter may reproduce megalospheric 

 broods, or give rise to swarmers, which by their (exogamous) 



