Foraminijera 95 



filled with seawater, or about 20 cc. of this material may be added to a 

 1 o-inch crystallizing dish. The dishes should be covered to prevent 

 excess evaporation and contamination. 



The water should be changed twice a day for the first few days, and 

 after that, once a day for a period of about two weeks. By that time 

 many Foraminifera will have crawled up the sides of the dishes and, if 

 a suitable substrate of diatoms has developed, several species should 

 have become established and reproductive activity begun. 



To establish persistent cultures of a single species, dishes should be 

 prepared with a suitable substrate of diatoms before the isolation and 

 transfer of the Foraminifera. Pure cultures of Nitzschia [see p. 34], 

 Navicula, or similar diatoms may be used for this purpose, or substrate 

 material may be used which has been taken from a dish in which the 

 Foraminifera have become established and in which the diatom substrate 

 is thin, uniform, and free from filamentous algae. If the latter method 

 is employed and no new material is added to contaminate the culture, a 

 single species of diatom will usually dominate the substrate in a short 

 time. 



The day after a foraminifer has reproduced asexually, the young, 

 which in some species number 200 or more, remain in the vicinity of 

 the parent tests. In establishing subcultures, several thousand individ- 

 uals may be transferred in a minimum of time by selecting these groups. 

 If this method is employed the age of the organisms will be known and 

 a maximum number of individuals of any stage of development will be 

 available at a given time. A convenient mouth pipette for handling 

 these organisms has been described (Myers, 1933). [see also pp. 43 

 and 70.] 



After the cultures are established, it is advisable to change the water 

 occasionally to compensate for evaporation and to replace nutrient mate- 

 rial removed by the organisms. A strong stream of water directed 

 against the sides of a dish by means of a glass syringe equipped with a 

 large rubber bulb will remove accumulated debris and help maintain a 

 thin clean substrate. 



Before seawater is added to a culture, the water to be added should be 

 filtered through a porcelain base Berkefeld or a sintered glass filter of 

 suitable porosity. Growth of diatoms may be influenced by controlled 

 illumination. When a subdued north light does not produce a suitable 

 growth, a few drops of a saturated solution of potassium nitrate may be 

 added to each culture or Allen and Nelson's (1910) modification of 

 Miquel's solution may be used. [See p. 33.] 



Temperature is a limiting factor in the distribution of species. In 

 cultures of Patellina corrugata there is a difference of only 4 to 5 C. 

 between the optimum and the upper thermal limit at which this species 



