1920] 



'Taylor: Neuromotor Apparatus in Euplotes 



421 



MACRONUCLEUS 



The outline and structure of the large C-shaped macronucleus 

 appears in the living, unstained organism very much as in the fixed 

 material figured and described by Yocom (1918). The "contraction 

 phase" of this organ with its reconstruction bands may be clearly 

 observed in animals free from too many food vacuoles. But these 

 features and particularly the granular, mesh-work consistency of the 

 macronucleus can be much more satisfactorily studied after the latter 

 has been dissected out witli the needle. It is then found to lie a highly 





Fig. B. The nuclei of Euplotes'. c.e., cut end; gn, eetoplasmic granules; mac, 

 macronucleus; mic, micronueleus; n.p., needle point. 



gelatinous, rather rigid structure composed of small granules imbedded 

 in a viscous, hyaline matrix (text fig. B). The organ is enveloped by 

 a very thin, structureless membrane. Upon exposure to the water, the 

 macronucleus increases slowly in size; within half an hour or so small 

 blisters of the membrane slowly appear over the surface; the rate and 

 extent of swelling increases and, upon rupture of the membrane in one 

 or several places, there follows a rapid dissolution of all except the 

 small granules, which for several hours exhibit a dancing Brownian 

 movement. These granules vary somewhat in size, with an average 

 diameter about one fourth that of the microsomes found in the 

 endoplasm. 



