PROTOZOA AND OTHER ANIMALS 949 



is a third skeletal element in Radiophrya; more or less numerous ecto- 

 plasmic skeletal strands attached along the entire inside of the V and 

 extending posteriorly on the ventral region of the body. These spread 

 laterally and, although usually restricted to the anterior part, may reach 

 almost to the posterior end. Skeletal elements of similar type are present 

 in. Mrazekiella (Fig. 202D) a.nd Meiaradwpbrya. 



The attachment organelle of Metaradiophrya asymmetYica, described 

 by Beers (1938a) from the terrestrial oligochaete Ehenia lonnhergi in 

 North Carolina, consists of a shaft embedded in the ectoplasm of the 

 anterior part of the body and a stout projecting hook, which Beers found 

 to be immovable (Fig. 202 A, B) . The left half of the V-shaped element, 

 such as is present in Radiophrya, is lacking. From the attachment organ- 

 elle, skeletal fibrils radiate in the ventral ectoplasm, very close to the 

 surface, the principal group originating near the base of the hook, fol- 

 lowed by an area of the shaft devoid of fibers, then a group of a few 

 short fibers at the posterior end. The asymmetrical arrangement of the 

 fibrils, which is contrasted with the bilaterally symmetrical systems of 

 M. falcifera and M. lumbvici, is the source of the specific name. 



In other forms the skeleton is completely or partly endoplasmic. In 

 Maupasella (Fig. 202F) the side arms of the V-shaped element have 

 become reduced and the point has developed into a prominent, project- 

 ing, pointed organelle, that serves for fixation. The longitudinal rays 

 have become endoplasmic. Related to Maupasella is Buchneriella crio- 

 drili Heidenreich, which has a particularly well-developed movable 

 spine (Fig. 202E). This penetrates into cells of the intestinal epithelium, 

 anchoring the ciliate firmly. In many ciliates torn from attachment, the 

 end of the spine was surrounded by a globule of differentiated host tissue. 



In Mesnilella the V-formed element is lacking, and the longitudinal 

 rays are endoplasmic and often reduced in number. A series may be ar- 

 ranged from a many-rayed condition (Fig. 20 2H) to that in which there 

 is only one spicule, reaching almost the full length of the body (Fig. 

 202G). 



IntoschelUna has a different type of skeletal apparatus (Fig. 2021). 

 It is an open ring in the ectoplasm surrounding the apex of the body. 

 From this ring three short spines project above the body surface an- 

 teriorly, and three extend in the ectoplasm posteriorly. Two of the 

 posterior spines are short; one, located at one end of the ring, is rela- 

 tively long. 



