THE FORAMINIFERA 119 



owing probably to the solvent action of the sea- water, they are 

 often reduced to fragments, or absent in bottom specimens. 



The Globigerina chambers contained in the Orbulina shell differ 

 from the free Globigerina bulloides in no respect, except in the ex- 

 treme thinness of their walls, and Rhumbler (38) is inclined to 

 separate the thin-walled shells hitherto classed under that species 

 as the young stages of Orbulina universa, d'Orb. Rhumbler also 

 points out, however, that in Globigerina bulloides, var. triloba, Reuss, 

 which is characterised by the large size of the three last chambers, 

 but not by the thinness of the shell, all variations are found be- 

 tween a terminal chamber which is folded back on its predecessor, 

 and one which completely envelops the other chambers, as in 

 Orbulina. The existence of these transitional forms in a variety 

 with a shell of the usual thickness raises the question whether the 

 Globigerina chambers enclosed in the Orbulina shell were so thin 

 when free, or owe their thinness to the action of the protoplasm 

 after their enclosure. 



However this may be, we have the fact that some specimens 

 classed as Globigerina bulloides end their individual existence in the 

 Globigerina form, while other specimens, little or not at all distin- 

 guished from them in the early part of their growth, become en- 

 veloped by an Orbulina shell. These have been classed under a 

 separate genus as Orbulina universa. The close resemblance between 

 these two sets of specimens in the early stages of growth, and also 

 between the Orbulina shell and that of the free Globigerina, in the 

 varying development of the spines and the surface sculpture, 

 strongly suggests that there is some more intimate relationship 

 between them than that of allied genera, but what its precise 

 nature may be is still very obscure. 



A large inflated terminal chamber is also found in Cymbalopora 

 bulloides, and in the littoral Pulvinulina lateralis, Terquem, and 

 these, like the Orbulina chamber, are also perforated by large 

 pores. Cymbalopora was taken in numbers by the Challenger, 

 as a pelagic form, in the neighbourhood of coral reefs, and, 

 according to Murray, every shell was filled with minute monadi- 

 form bodies. 1 This observation would suggest that the inflated 

 chamber may go with the megalospheric form, bulb though 

 Rhumbler finds a single large nucleus in all the specimens of 

 Orbulina he examined, the same was true of the free Globigerinae. 

 The size of the central chamber of the included test of Orbulina 

 varies, according to Schacko (39), from 16-23 /* in diameter, 

 while in the free Globigerina it varies from 7-20 /*. Neither in 

 the size of the central chamber, nor in the character of the nuclei, 

 therefore, have we at present direct evidence for dimorphism 

 among these animals. As to the modes of reproduction of Globi- 

 1 Brady (3), p. 639, footnote. 



