AN AMICRONUCLEATE OXYTRICHA 477 



Specimens for cytological study were fixed in corrosive sub- 

 limate (saturated solution) with 1 per cent acetic acid and in 

 Schaudinn's sublimate-alcohol (strong). Various stains were 

 tried, including Heidenhain's iron hematoxylin, Delafield's 

 haematoxylin, borax carmine and picro-carmine. Differentiation 

 was made with acidulated alcohol (70 per cent alcohol and 0.01 

 per cent HCl). In general Delafield's hematoxylin has been 

 found to give the best results. Eosin and tetra-brom-fluorescic 

 acid were used as counterstains, the latter being especially good 

 for staining external structures as cilia, cirri, and membranelles. 



Single animals were fixed and stained on depression slides. 

 The animal was kej^t under observation during the whole process 

 except for the period necessary for staining, when the slide con- 

 taining the specimen was placed in a moist chamber. The 

 various fluids used in the process were drawn off with a capillary 

 pipette or filter-paper, the only transfers being when the animal 

 was isolated for fixation and when the same animal, now ready 

 for mounting, was placed on a thin glass slide. Specimens 

 were cleared and mounted in cedar oil or in xylol and damar. 

 Total mounts thus made were prevented from being crushed 

 by placing pieces of hair of suitable lengths under the cover-slips. 

 At various times smears of large numbers of animals were made 

 for general study. Sections, 4 // in thickness, have been prepared, 

 but it has been found that study of these has added nothing 

 to the cytological details which on account of the thinness of the 

 animal may be studied thoroughly in total mounts. 



3. STUDY OF THE NORMAL ANIMAL 



Although hypotrichous forms have been carefully investigated, 

 no worker has as yet been able to breed these cihates indefinitely 

 by the daily isolation method without conjugation. Maupas 

 ('88) carried cultures of Stylonychia pustulata without conju- 

 gation for 316 generations ; Stylonychia mytilus, similarly, for 319 

 generations; Onychodromus grandis and Oxytricha for 320 to 

 330 generations. He concluded that in all these cases death was 

 due to old age, no opportunity having been allowed for 'rejuve- 

 nation' by conjugation. Joukowsky ('98) kept one of four 



