120 J. J. LISTER. 



with it ; they are, however, exceedingly slender. The chambers 

 composing it may be as many as thirteen. The diameter of the 

 apical chamber varies from 16 to 23 /x. 



ScHACKO found some small bodies "resembling in shape 

 and size " the first two chambers of the Globigerina, especially 

 abundant in the terminal chamber of the latter. These he 

 regarded as young. 



In April, 1884, Schlumberger (34) presented a note to the 

 Academic des Sciences in which he urged the view that the 

 empty OrhuHna shell and that with Globigerina-\ike contents, 

 were dimorphic forms of the same species, comparable with the 

 forms which had been shown to exist in the species of Num- 

 mulites and Miliolids. After reviewing the evidence he 

 proceeds as follows (p. 1004) : — " La loge unique de VOrhulina 

 est I'homologue de la loge initiale des autres Foraminiferes : 

 lorsqu'elle reste vide, elle est de la forme A; avec la sdrie de 

 logos internes elle est de la forme B." 



Schlumberger concludes with the remark that the case of 

 Orbulina is in favour of the view that the forms A and B are 

 distinct from their origin. 



The ascertained facts appear to be as follows : — 



In a sample of the shells of Orbulina many of the in- 

 dividuals are simple empty spheres varying in size, and the 

 largest shells of the sample are of this character. In others, 

 the interior of the sphere is more or less completely occupied 

 by a spire of chambers closely resembling a free Globigerina 

 shell. This is firmly attached to the wall of the investing 

 spherical chamber. In rare instances (e, wood-cut) the Orbulina 

 chamber does not completely enclose the Globigerina chambers, 

 and in that case the outer spherical surface of the Orbulina is 

 interrupted by the prominences formed by the terminal 

 chambers of the Globigerina. Usually the Globigerina shell is 

 remarkable for the extreme tenuity of its walls and spines, but 

 when portions of it are not enclosed by the Orbulina shell, they 

 are found, as Schlumberger points out, to be thick walled, 

 while the enclosed portions are thin (e). 



The Globigerina chambers are usually most perfect when 



