180 The Philippine Journal of Science i9i8 



environment in which they live. A recent paper by Hausmann ^ 

 contains some excellent hints for collecting and studying fresh- 

 water protozoa. Directions for collecting rhizopods are given 

 by Leidy ^ in his great monograph, but are not so detailed as 

 those given by Hausmann. 



Material collected from natural sources should be studied as 

 soon after collection as possible, especially if an enumerative 

 study is to be made. Frequently striking morphological changes 

 manifest themselves after protozoa have been transferred from 

 their natural environment to artificial culture media, and studies 

 of morphology and physiology made in artificial media should 

 be carefully controlled and interpreted with great caution. 



Cultivation. — In principle the successful cultivation of proto- 

 zoa involves the discovery of the kind of food upon which the 

 organism subsists and then supplying it with that food. This 

 is often easier said than done. In the case of the parasitic 

 forms the problem is particularly difficult; and many of them, 

 especially the tissue-dwelling forms, have not yet been cultivated. 

 As to nutrition the free-living forais may be holozoic, holophytic, 

 or saprozoic. A given species may at one time be nourished by 

 the holophytic method and later by the saprozoic; or nutrition 

 in another may at one time be holozoic and at another saprozoic. 

 Lauterbom " has applied the term "sapropelic" to a characteristic 

 fauna living under conditions of saprozoic and partly holozoic 

 nutrition. These forms are found in fresh-water mud or ooze 

 composed largely of the decaying remains of dead plants and 

 similar debris. There are many predacious forms that feed 

 wholly on other protozoa, and that must be distinguished from 

 those that live on bacteria. Many of these predatory forms 

 feed on some particular species and apparently select their food 

 with great care. For instance, Didinium nasutum lives on 

 Paramecium; Spathidium, spathula, on Colpidium colpoda; Acti- 

 nobolus radians, on Halteria grandinella, and so on. In the 

 absence of the species that furnishes them with food they will 

 quickly starve or encyst. 



A large variety of fresh-water forms will live well in hay- 

 infusion media. This may be prepared by boiling 1 gram of 



• Hausmann, L. A., Observations on the ecology of the Protozoa, Am. 

 Naturalist (1917), 51, 157. 



' Leidy, Joseph, The Fresh Water Rhizopods of North America. Repts. 

 U. S. Geol. Surv. of the Territories. Government Printing Office, Washing- 

 ton, D. C. (1879), 12, 8. 



' Lauterborn, R., Die "sapropelische" Lebevvelt, Zool. .Anz., Leipzig 

 (1901), 24, 50. 



