168 J. J. LISTER. 



A specimen of the megalospheric form oiPolystomella crispa 

 (Linn.) is described above whose protoplasm was broken up 

 into small round spores of uniform size, and I have seen such 

 uniform spores escape from the broken shell of a specimen. The 

 Euglena-\\ke bodies, described by Schneider (37), may possibly 

 have been of the same nature. 



When the existence of dimorphism in the species of Fora- 

 minifera was brought forward by Munier-Chalmas, it was, as 

 we have seen, supposed that the microspheric form was a modi- 

 fication of the megalospheric. It was suggested that when the 

 megalospheric form attained a certain size an absorption of the 

 central chamber occurred in some individuals, the space which 

 it had occupied being then filled in by small chambers, while 

 additional chambers were added at the outside of the shell. 

 Small megalospheric forms would thus be converted into the 

 large microspheric forms. 



De Hantken and DE LA Harpe (15), and more recently. 

 Van den Broeck (5), have brought forward strong reasons for 

 rejecting the hypothesis that the microspheric form is produced 

 by modification of the megalospheric. 



In the genus Biloculina among the Miliolidse, as Schlxjm- 

 BERGER has shown, the plan of growth of the chambers imme- 

 diately succeeding the central chamber differs entirely in the 

 two forms {cf. the woodcut on p. 114), and this difference produces 

 an effect on the form of the ultimate chambers. As in the case 

 of the two forms of the Nummulites cited by DE Hantken and 

 DE LA Harpe the hypothesis would imply a remodelling of the 

 whole shell. Again, in the bi-concave discs of Orhitolites the 

 centre of a megalospheric individual is three times as thick as 

 that of a microspheric. Hence to convert the megalospheric 

 form into the microspheric, not only the primitive disc but 

 many of the inner rings of chamberlets must be absorbed and 

 replaced by fresh ones. 



