201 



the shells, and so rendered them more buoyant. After the 

 floatings have been secured, the next step is to separate the 

 heavier sj>ecimens from the sand. In order to do this the 

 material from the bottom of the beaker is poured out into a 

 shallow tray, such as a " half-plate " developing dish, and covered 

 with about an inch of water. The dish is then taken up and 

 rocked gently with a sort of circular sweeping motion. This 

 rocking action of the water causes the light calcareous particles 

 to rise to the surface of the layer of heavy sand-grains, and to 

 collect in eddies. At the proper moment, which is quickly 

 learned by experiment, the water is rapidly poured off into a 

 sieve, and carries the Foraminifera and other light organisms 

 with it. The process is repeated until nothing but sand is left 

 in the dish. The material in the sieve is then carefully dried, 

 and can be preserved for an indefinite period if kept in dry tubes. 

 Dredgings and silt can be cleaned in the same manner ; but if 

 much mud is present it should first be removed by washing the 

 material over a sieve of very fine gauze (120 to 150 meshes per 

 inch) under a tap of gently running water. This allows the 

 mud to pass away, leaving the sand and forams behind. The 

 residue can then be treated in the manner already described. 



After dealing with some of the characteristic features of the 

 group, Mr. Earland described at some length the dimorphism 

 of the Foraminifera. The term "dimorphism" was originally 

 used to describe a change in the method of the arrangement of 

 the chambers during the lifetime of an individual. Thus, a 

 specimen of the genus Bigenerina commences its existence with 

 chambers arranged biserially, and subsequently changes to 

 chambers arranged in a single row. The word was, however, 

 now used in a different sense, and referred only to the difference 

 in the size of the first or " primordial " chamber of the test. It 

 was noticed many years ago that ISTummulites in various fossil 

 deposits were often associated in "pairs of species," one species 

 being small and the other large, and that the smaller 

 species always had a large primordial chamber, while the larger 

 species had a very tiny one. To account for the fact, De la 

 Harpe enunciated a " Law of the Association of Species in 

 Pairs." Subsequently, Munier-Chalmas expressed the opinion 

 that these pairs were but forms of the same species, and called 

 the form with the large primordial chamber (inegolospheric) 



