90 



AN INTRODUCTION TO THE STUDY OF FOSSILS 



Globigerina (Fig 31). Triassic to present. 



This differs from Amoeba in the possession of a calcareous 



support, the test. This test is composed of several globular 



chambers arranged in an irregular spiral (whence the name from 



Latin globus, a ball, + gererc, 

 to carry). It also differs from 

 Amoeba in the length and delicacy 

 of pseudopodia, which unite with 

 each other at intervals. The 

 chambers are somewhat glassy 

 in appearance, and are pierced 

 by numerous microscopic pores 

 through which, as well as through 

 the large opening from the largest 

 chamber, the pseudopodia are ex- 

 tended. The protoplasm is per- 

 fectly continuous throughout all 

 the chambers. The food consists 

 mostly of microscopic plants, such 

 as diatoms and algae, more seldom 



of the minute copepod crustaceans; these are enveloped and 



digested by the net-like pseudopodia. 



Globigerina typically lives floating at the surface of the 



ocean, spreading out its pseudopodia in all directions around 



it. At the death of the individuals, the tests fall to the sea 



bottom, and accumulate in vast layers, forming the globigerina 



oozes. 



Although known from the Triassic to the present, it occurs 



but sparingly in the Mesozoic. 



Fig. 31. — The lime-secreting pro- 

 tozoon, Globigerina ccqiiilateralis 

 Brady, from the Gulf of Mexico. 

 This species is world-wide in its 

 distribution, in both tropical and 

 subtropical waters. Three views 

 of the same specimen (much en- 

 larged). The greatest mass of 

 protoplasm was extended through 

 the large opening (0). 



1. Examine the specimens under the compound microscope 

 (these should include thin sections of chalk, and some globig- 

 erina ooze or sand scraped from such shells as those from 

 the Paris Basin, from sponges or from corals). 



2. Sketch (a) Globigerina, {h) Textularia (Pennsylvanian to 

 present), usually cone-shaped with two rows of alternating, 



