96 GARY N. CALKINS 



MATERIAL AND METHOD 



After many attempts to find a form sufficiently large and hardy 

 for successful experimental merotomy, Uronychia transfuga 

 Stein was finally selected. This is one of the hypotrichous ciliates 

 belonging to the family Euplotidae. The Roscoff form differs 

 in some minor respects from the species described by Stein, but 

 as the organism is somewhat polymorphic and shows such wide 

 differences in size and appearance, I would not venture to make 

 a new species. The band-form nucleus characteristic of the 

 family is here replaced by a chain of large nuclear spheres during 

 the vegetative stages, but these coalesce during division to form 

 the typical band. The organism is somewhat longer than broad, 

 with bluntly rounded anterior and posterior ends, and is elliptical 

 in shape. The hardened ectoplasm forms a practical cuirass 

 about the cell and gives to the latter much of its durability. The 

 dorsal surface is slightly arched and sculptured on the anterior 

 margin for the insertion of the membranelles of the adoral zone, 

 while posteriorly it is deeply cut out for the posterior cirri. The 

 latter are separated into two groups by a posterior process or 

 lobe of the dorsal surface (fig. 1). To the left of this lobe originate 

 two large and one small cirri, one of the larger cirri being dorsal 

 to the other large one. On the right side of the lobe are seven 

 cirri of variable size. Three of these are inserted dorsally and 

 are sharply curved, sickle-like towards the left. The bases of all 

 three of these are in a line and the extreme left one lies partly 

 on the dorsal lobe. A similar set of three cirri originate on the 

 ventral surface, opposite the dorsal set, but unlike the latter, 

 the cirri are straight or but slightly curved. One large cirrus, 

 also curved sickle-form to the left, arises between the two sets of 

 three and on the extreme right edge. Two smaller cirri arise 

 on the right margin and one or two small ones originate on the 

 ventral surface (fig. 1). 



The adoral zone of Uronychia consists of large membranelles 

 running from the anterior right margin, around the anterior 

 margin and then ventrally in a broad curve to the mouth. The 

 membranelles are inserted in the serrations of the anterior mar- 



