ON THE LIFE-HISTOBY OF THE FORAMINIFEBA. 121 



the investing chamber is small, the larger this chamber is the 

 less perfect are the contained chambers. In dead specimens 

 these are frequently represented by a mass of broken fragments. 

 In the largest Orhulinas no trace of contained chambers is 

 found. 



A small chamber whose diameter varies, according to 

 ScHACKO, from 16 to 23/t is frequently found at the apex of the 

 spire of chambers. 



While the Globigerina chambers are perforated by small 

 apertures of uniform size, the pores of the Orbulina are of two 

 sizes. 



It not unfrequently occurs that the Orbulina shell is double 

 or even treble, the spheres being contained one within the 

 other, and unattached, as in a Chinese carving. 



Before discussing the evidence, it will be well to recall the 

 mode of life of Orbulina. 



In common with the rest of the family Olobigerinidce, and 

 species of the genus Pulvinulina among the Botalidce, Orbulina 

 is frequently found leading a pelagic existence at or near the 

 surface of the sea. When taken in the tow-net, it is often 

 beset with long spines which may be more than three times 

 the diameter of the shell in length. When the protoplasm is 

 extended a thick vacuolated layer invests the shell and the 

 bases of the spines. 



The fact that all transitional stages are found between 

 small Orbulina shells containing a perfect spire of chambers, 

 and large ones which are empty, appears to point to the 

 conclusion that the empty Orbulina shells when small contained 

 such chambers. 



What is the relation between the Orbulina shell and the 

 contained chambers? The suggestion that these constitute 

 a young individual about to be set free is incompatible with 

 the facts (1) that they are attached to and sometimes involved 

 in the Orbulina shell ; (2) that they are often seen in stages of 

 degeneration; and (3) that the largest Orbulina shells are 

 empty and complete. 



According to Major Owen's view, the outer sphere may be 



