ON THE LIFE-HISTORY OF THE FORAMINIFERA. 123 



of the Globigerina chambers included in Orhulina. In 63 

 surface specimens of Olobigerina mounted in balsam, in the 

 Brady Collection, the mean diameter of this chamber varies 

 from 7 to 20 fi, the most frequent diameters being 14 and 17 fi. 

 ScHACKO gives the diameter of the first chamber of the 

 Globigerina enclosed in the Orhulina shell as 16 to 23 /a. So 

 far as this rather scanty evidence goes, then, it appears that there 

 is no evidence of dimorphism in the central chambers of these 

 forms. 



It will be shown below that in the species which I have 

 examined the two forms are as sharply distinguished by the 

 character of their nuclei as by the size of the central chambers. 

 The only evidence on this head with which I am acquainted 

 is that of one specimen of a free Globigerina bulloides with 

 eight chambers, described by R. Hertwig (17), in which a 

 single large nucleus was present. From analogy it would 

 appear that this specimen was megalospheric. 



Further evidence on the nature of the nuclei of Orbulina 

 and Globigerina would no doubt throw light on the question of 

 their relationship. 



(c.) Nuclei. 



Our knowledge of the nuclei of Foraminifera is mainly 

 derived from the descriptions of R. Hertwig, F. E. Schulze, 

 and 0. BiJTSCHLi. 



The evidence is for the most part of a fragmentary character, 

 but it may be convenient to bring it together. The observa- 

 tions which I have met with are here arranged under the names 

 of the families. 



I. Gromidce.— In Gromia, Max Schultze ((38), p. 22) 

 found a single nucleus in young specimens, and from two to 



sixty in old ones. 



II. Miliolidw.—In Quinqueloculina fusca, F. E. Schulze 

 ((41), p. 136) described an oval body which he took for the 

 nucleus, 



