450 University of California Publications in Zoology [Vol. 20 



polychrome blue and orcein, Prenant's triple; and as counterstains 

 after haematoxylin : eosin, erythrosin, light green, methyl green, 

 methylene blue, Congo red, Bordeaux red, grange G, and safranin. 

 As nuclear stains, none has been as satisfactory as the aqueous and 

 alcoholic iron-alum haematoxylins ; of the counterstains, Bordeaux 

 red, eosin, methylene blue, orange G, and light green have produced 

 good results. 



As special stains for rhizoplasts and basal granules of flagella, a 

 weak solution (0.1 per cent) of Bordeaux red, as recommended by 

 Rhodes (1919), and the solution of Gicklhorn (1921) have been used 

 before staining in iron-haematoxylin. The organisms were stained 

 for twelve to thirty-six hours in either of these solutions and then 

 transferred directly to iron-alum. Both stains are good, but the use 

 of Bordeaux red has been especially advantageous. 



GENERAL MORPHOLOGY 



Menoidiuin incurvum is characterized by a rigid, elongate bean- 

 shaped body (pi. 40, fig. 1), ranging in length from 15 to 25/t. Even 

 under a 4 mm. objective the surface of the living flagellate shows 

 regularly spaced longitudinal striations which are some distance 

 apart (pi. 40, figs. 1 and 6). As determined by a study of optical 

 cross-sections in stained material, the number of these varies from 

 ten to fifteen for flagellates whose nuclei are in the prophase or 

 resting stage ; the greater number of those examined possess fourteen 

 striations. The number of these striations is correlated with the 

 circumference of the organisms; as the flagellate enlarges with the 

 approach of binary fission, the number is seen to be increased (pi. 40, 

 fig. 2). Posteriorly the striations converge to a point (pi. 40, fig. 3) ; 

 anteriorly they extend to the margin of the gullet (pi. 40, fig. 4). In 

 optical cross-sections (pi. 40, fig. 5) their thickness is approximately 

 the same as that of the region between them, so that they probably 

 do not represent appreciably thickened parts of the pellicle. 



The endoplasm contains a variable number of plastids (pi. 40, 

 figs. 1 and 6), ranging from practically colorless to a very light green; 

 these were not stained in any of the stains used and are probably 

 paramylum bodies, since they appear tinged with yellow when 

 treated with solutions of iodin. In the living flagellates these plastids. 



