158 J. J. LISTER. 



protoplasm. In Orbitolites, however, the nucleus in the pri- 

 mordial chamber is hardly larger in the examples with many 

 rings of chambers than in those with few. 



The Celebean specimens are in a phase of growth to which 

 I have found no analogy in Polystomella. 



The account of the nuclei of Orbitolites here given differs 

 from that of Professor Butschli in which numbers of minute 

 and irregular nuclei are described scattered through the proto- 

 plasm. Possibly his examination was confined to such later 

 stages of megalospheric specimens as those which I obtained 

 from Tonga, in which, as above described, the nuclei are found 

 in this condition. 



(c.) Rotalia Beccarii (Linn.). Figs. 38-40. 



Among seven examples of this species, six were megalo- 

 spheric, and one microspheric. 



MiCROSPHERic Form. In the representative of this form 

 there are thirty-two chambers. The microsphere measures 13 /i 

 in diameter (fig. 38). Some twenty-four nuclei are present, 

 irregularly distributed through chambers 10 to 25. As in 

 Polystomella, the nuclei increase in size from within outwards. 

 I see no " stained strands," but the protoplasm of the imme- 

 diate neighbourhood of some of the nuclei has taken a diffused 

 flush*. 



Megalospheric Form (fig. 39). The mean diameter of the 

 megalosphere varies between 37 and 65 fi, having an average of 

 54 6 /i. In the four cases in which the protoplasm is preserved, 

 a single large nucleus is present, situated some distance behind 

 the middle point of the protoplasm. In one case it is drawn 

 out into the succeeding chamber, in the other three whose nuclei 

 are round or oval, the mean diameter of the nucleus varies 

 between 27-5 and 33 fi. In each case fairly large nucleoli are 

 present (fig. 40). 



As stated in Postscript 2, I have observed the production of megalospheric 

 young by a microspheric parent in this species. 



