28 University of California Publications in Zoology [Vol. 20 



one included witliin the undulating membrane as its marginal fiber 

 (m. fl.) and carried out beyond the projecting tip of the parabasal 

 body as a bit of free flagellum. The anterior flagella usually exceed 

 the body in length. The posteriorly directed location in our figures 

 is merely for spatial accommodation, an anterior direction being usual 

 in life. 



The undulating membrane (fig. A, 5, und. mem.) is attached to the 

 left side of the body (fig. A, 1) in a sweeping C- or S-shaped curve 

 reaching to the posterior end of the body (fig. A, 4, 6 ; pi. 3, figs. 1, 14) . 

 It exceeds the length of the body two to three times in some small 

 sehizonts (pi. 4, fig. 30). The coiling into the S-shaped forms appears 

 to be an accommodation of the somewhat rigid but elastic parabasal, 

 when longer than the body, to its location within the cytoplasm. 

 The membrane always follows the course of the parabasal and remains 

 adherent to it upon cytolysis (pi. 3, fig. 11). In one ease (pi. 3, fig. 4) 

 a detached membrane consisting only of the marginal flagellum and 

 the fold of the protoplasmic pellicle running from the parabasal around 

 the flagellum, was found free in a smear preparation. The membrane 

 and flagellum are thrown into twelve to twenty subequal, subequi- 

 distant waves of contraction which fade out in the distalmost end. 



The parabasal body (fig. A, 5, par. h.) is a rigid, elastic, deeply 

 staining, ehromatoidal rod lying at the base of the undulating mem- 

 brane in the peripheral plasma of the body. Its C- or S-shaped course 

 appears to determine the direction of that membrane. Its length 

 usually exceeds that of the body by 10 to 25% and its diameter, 

 2 to 3.5/x, is greatest somewhat anterior to its middle. From this 

 region it tapers gradually toward either end, terminating anteriorly 

 at the centroblepharoplast (fig. A, 6), or in mitosis at the blepharo- 

 plast proper (fig. A, 5), and posteriorly at its junction with the 

 marginal flagellum which projects beyond their union for a short dis- 

 tance as a free lash. It stains densely with haematoxylin and con- 

 stitutes the dominating feature of the organism in all preparations 

 and in life. It shows in stained sections (pi. 3, figs. 3 and 3a) a 

 differentiated structure consisting of an outer deeplj' staining shell 

 less than a fifth of its diameter in thickness and a less deeply stained 

 core. This core is traversed by wedgelike discs of the cortical sub- 

 stance, wliich ai'ise principally on the concave face and fade away 

 towards the opposite side. 



We have elsewhere (Kofoid and Swezy, 1915; Kofoid, 1917) inter- 

 preted the parabasal body as a reservoir of substances utilized by the 

 neuromotor svstem in motor activities. It is obvious on observation 



