CHAPTER X 



TRIMORPHISM 



This work would be incomplete without a short discussion of 

 the phenomena to which the name Trimorphism has been given 

 by Hofker. The microspheric and megalospheric forms have 

 already been discussed in some detail. There may be more than 

 one development of the megalospheric form between two genera- 

 tions of microspheric ones. The size of the megalospheric pro- 

 loculum in these intermediate generations is not constant, and 

 the resulting test lacks some of the early stages. With the 

 largest megalospheric proloculum, the adult characters are taken 

 on almost at once. With the smaller megalospheric proloculum, 



Figs. 1—3. Idalina antiqua (d'Orbigny). (After Munier Chalmas 

 and Schlumberger). Fig. 1. Section of microspheric specimen with 

 quinqueloculine early stage followed by triloculine and biloculine stages. 

 Fig. 2. Section of megalospheric specimen with triloculine early stage 

 followed by a biloculine stage, the quinqueloculine stage skipped. Fig. 

 3. Section of a megalospheric specimen with the biloculine stage fol- 

 lowing the proloculum, the triloculine and quinqueloculine stages 

 skipped. Figs. 4—6, after d'Orbigny. Fig. 4. Microspheric form 

 "Murginulina hirsuta d'Orbigny." Fig. 5. Megalospheric form 

 "Dentalinafloscula d'Orbigny" Fig. 6. Megalospheric form "Nodo- 

 saria aculeata d'Orbigny." 



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