INTRODUCTION. 33 



rare and curious Ciliophrys infusionum is that, neces- 

 sarily or otherwise, it most frequently occurs in water 

 which has been kept two or three weeks in association 

 with fragments of pond- vegetation. The occurrence of 

 particular species, year by year, in the same ponds, is 

 not, however, to be relied upon. 



An aquarium, in which some fine-leaved plants, e. g. 

 Hottonia palustris, Utricularia vulgar is t and Ranun- 

 culus aquatilis, are kept growing without being often 

 disturbed, is a valuable adjunct to the study of the 

 Rhizopoda. 



PRESERVATION. 



By the employment of dilute nitric acid or sulphuric 

 acid it is possible to isolate the Rhizopod nucleus; 

 when carmine staining renders a study of that organ 

 quite practicable. The process, however, is a delicate 

 one. Dr. Eugene Penard has, by the exercise of much 

 care and patience, preserved in suitable media numerous 

 examples for reference. Where they can be made, 

 permanent preparations are no doubt desirable and 

 useful, inasmuch as they facilitate a study of the 

 nuclear structure under high powers of the microscope, 

 but the ordinary student will probably be content to 

 make careful drawings from living examples, in different 

 aspects and under varying conditions of their existence. 

 These, together with descriptive notes, should in all 

 cases be preserved. 



The transparent tests of some of the Conchulina, 

 when freed from extraneous matter, may be preserved 

 in glycerine jelly, and the gritty tests of various species 

 of Difflugia can be mounted as opaque objects in the 

 same manner as Foraminifera. Beautiful examples, 

 obtained by repeated washings of the mud from a 

 pond at Chipperfield, Herts, have been obtained by Mr. 

 Arthur Earland, showing that this method of treating 

 the Difflugite is feasible and yields good results. 



