The Sarcodina 217 



(sometimes multiples of twenty) rods which form a characteristic pattern. 

 An equatorial group emerges from the body in a plane essentially 90° 

 from either pole, and two other groups emerge in planes about 45° above 

 and below the equatorial plane. The basic skeleton is sometimes modified 

 by lateral outgrowths from the rods which form a perforated shell, com- 

 posed typically of twenty plates. Two such shells, concentric with the 

 central capsule, are present in certain species. The outer layer of extra- 

 capsular cytoplasm is joined to the skeletal rods, apparently by contrac- 

 tile fibrils ("myophrisks") which are said to bring about minor changes 

 in form and volume of the body (Fig. 5. 9, B, C) and thus to aid in 

 controlling flotation. 



The suborder includes such genera as the following: Acantlwcliiasma Krohn, Acan- 

 thometm Midler (Acaiithoinetron Haeckel) (94; Fig. 5. 9, A), AcantJionia Haeckel, 

 Actmelius Haeckel, Amphilonche Haeckel, Diplocolpus Haeckel, Diploconus Haeckel, 



Fig. 5. 12. A-C. Skeletal features of Monopylina: tripod and central cap- 

 sule (A); tripod and ring enclosing central capsule (B); helmet-like skeleton 

 (cephalis, capitulum) derived from the more primitive tripod and ring (C); 

 schematic (after Haeckel). D. Helmet-like skeleton of Eucyrlidium cranioidcs 

 Haeckel, xllO approx. (after H.). E. Skeleton of Dictyophimus gracilipes 

 Bailey, schematic (after Bernstein). F. Lithocircus annularis Hertwig, skel- 

 eton, central capsule with perforated plate, nucleus (in outline); schematic 

 (after H.). 



