180 ON THE LIFE-HISTORY OF THE FORAMINIFERA. 



the Orbulina with a segment of another globe added to its 

 surface. 



But there are other specimens of Orbulina found occa- 

 sionally in the Dogs Bay sand which have a very special 

 interest. D^Orbigny divided the shells of the Foramini- 

 fera primarily into two groups, according as they were 

 formed of one or of many chambers, the former being 

 called monothalamous and the latter polythalamous shells ; 

 but this division, though apparently so natural, has proved 

 .unsatisfactory, its effect being in many cases to separate 

 widely apart forms which are closely related ; but in no 

 case is it more clearly shown to be untenable than in Or- 

 bulina and Globigerina, which are proved, I believe, by the 

 specimens now to be described, to be simply different states 

 of one and the same species. That this is the case was 

 announced in 1858 by L. F. Pourtales in 'Annals and 

 Mag. of Nat. Hist.,^ his specimens illustrating the fact 

 having been obtained from dredgings in the Gulf Stream. 

 Dr. Carpenter mentions this announcement, but, after 

 stating that he had himself looked in vain for appearances 

 like those described, gives reasons why, as he believes, the 

 observations are not likely to be correct ; these reasons, 

 however, are not unanswerable, and they lose their weight 

 altogether in face of the specimens themselves, which show 

 most indisputably the perfect Globigerina inside the sphere 

 of the Orbulina (Plate IV. fig. i). Pourtales explained this 

 appearance by supposing that the Globigerina is the young 

 of Orbulina, and is developed within it, untd at last the 

 parent-shell breaks to allow its escape ; but there are many 

 specimens from Dogs Bay which will not admit of this ex- 

 planation, though they suggest a different one, and this 

 equally applicable to them all. In the peculiar specimens 

 to which I allude (Plate IV. fig. 2), the external appearance 

 is that of a sphere made irregular by several rounded pro- 

 jections, or portions of smaller spheres ; but when they are 



