6 University of California Publications in Zoology [Vol. 18 



plasm in the caudal area; a pair of caudal flagella which arise from 

 the posterior tip of the axostyle or axostyles ; and a pair of free ven- 

 trals, arising upon the axostyle a short distance back from the ble- 

 pharoplasts. Basal granules are sometimes visible at the posterior end 

 of the axostyle, and where the free parts of the anterolateral flagella 

 emerge from the cytoplasm (pi. 1, fig. 2). 



The separate structures enumerated above may now be treated 

 more fully, as to structures, position, and possible function. 



The two oval-shaped nuclei lie on either side of the axostyle in the 

 cytostomal area. In the resting stage (pi. 1, fig. 1) each nucleus con- 

 tains a central ovoid karyosome surrounded by a hyaline space, which 

 in turn is enclosed by a very definite nuclear membrane. I could find 

 no signs of peripheral chromatin in the nuclei. The major axes of 

 the nuclei are slightly directed toward each other anteriorly. The 

 karyosome is connected to the centrosome on the nuclear membrane at 

 the anterior pole by a small intranuclear rhizoplast ; and the centro- 

 some in turn is connected with the blepharoplast by a small extra- 

 nuclear rhizoplast (pi. 1, fig. 1) . By means of these rhizoplasts and the 

 anterior commissure, the nucleus, centrosome, blepharoplast, and flag- 

 ella of one side are connected with those of the other side, thus form- 

 ing one integrated system, designated by Kofoid and Christiansen 

 (1915) as the neuromotor system. 



The centrosome of each nucleus, previous to division, varies in size ; 

 it lies on the nuclear membrane at the anterior pole of the nucleus. 

 The centrosome of each nucleus is connected by a slender rhizoplast 

 with the nearest blepharoplast at the head of the axostyle. When the 

 axostyle splits, the anterior commissure may for a time remain intact, 

 thus connecting the blepharoplasts of each new axostyle head; and 

 when the axostyle is not split it appears as a fibril making possible 

 the establishment (pi. 1, fig. 1) of direct connection between the karyo- 

 some of one nucleus and the karyosome of the other nucleus. A 

 paradesmose was best demonstrated with Mallory's connective tissue 

 stain ; this fibril connects the two divided centrosomes of each nucleus 

 and always lies outside of but closely applied to the nuclear mem- 

 brane (pi. 1, figs. 5, 6, 7). It is a recurrent cell organ in this species. 



The two blepharoplasts united by a fibril, the anterior commissure, 

 lie embedded in the material at the head of the axostyle. The blepharo- 

 plasts appear to initiate mitosis, for they are the first organelles to 

 divide and are followed by the cleavage of the axostyle. That this is 

 the case is evidenced by the large number of forms having a partial 



