386 University of California Publications in Zoology [Vol. 18 



SUMMARY 



This study of Euplotes patella has brought out the following 

 interesting and significant facts: 



1. Euplotes patella is oval in form, concave ventrally, convex 

 dorsally. The ventral surface is characterized by the presence of a 

 large triangular cytostome, the dorsal part of which continues forward 

 and forms the anteriorly projecting lip ; a cytostomal diverticulum, 

 nine ventral, five anal, and four marginal cirri ; a series of mem- 

 branelles extending along the left side of the cytostome and continu- 

 ing forward around the anterior end dorsal to the anterior lip. The 

 whole body is covered by a firm cuticle. The dorsal side is marked 

 by eleven rows of granules arranged in rosettes. 



2. A neuromotor apparatus is present in Euplotes patella. This 

 structure is composed of a motorium, the probable center of coordina- 

 tion, to which are joined five fibers from the five anal cirri and a 

 fiber which connects with the inner ends of the cytostomal membra- 

 nelles, and a lattice-work structure in the anterior lip which connects 

 with the fiber around the anterior end. This system has a probable 

 nervous function, as is evidenced by its structural relations to the 

 motile parts of the organism. The ventral and marginal cirri have a 

 number of fine fibers radiating out from their bases. Their function 

 is not clearly understood, but they probably represent a detached 

 dissociated neuromotor apparatus. 



Observations show that there is a coordination between the move- 

 ments of the five anal cirri and the cytostomal membranelles. Vigorous 

 movements of the cirri are accompanied by increased activity of the 

 membranelles. Certain reactions to stimuli indicate that the anterior 

 end is very sensitive to touch. Such coordinated movements and 

 response to stimuli indicate that the neuromotor apparatus is a struc- 

 ture which functions as a coordinating mechanism, having the function 

 of transmitting both motor and sensory impulses, over a system as yet 

 undifferentiated into motor and sensory nerves. 



3. The micronucleus undergoes mitosis and each daughter nucleus 

 becomes the micronucleus for the daughter Euplotes resulting from 

 binary fission. The macronucleus undergoes progressive reconstruc- 

 tion, beginning at the two ends and migrating toward the middle. The 

 latter periods of this reconstruction are accompanied by a contraction 

 of the M^hole macronucleus. This contraction is not unlike synizesis 



