EXPLANATION OF PLATE IL 



PLEXAURELLA DICHOTOMA. 



Fig. 1. Small zoanthodeme^ reduced one- half . 



Fk;. 2. Lii'ing and expanded polyp as it appears from above: a. a. a, tentacles; 



b, b, body wall showing through as a light circle; c, c, mesenteries 



showing through as light lines radiating from oesophagus to body wall ; 



d, mouth; e, e, e, tentacular papilla-. 

 Fig. 3. Cross-section of branch of zoanthodenie : a, a, expanded polyp; b, b, b, 



b, retracted polyps; c, empty calicle; d, d, ccenenchyma in which 



spicules are embedded; e, e, e, e, eight primary water-vascular canals; 



f, semi-calcareous portion of axis cylinder; g, corneous portion of axis 



cylinder, h, h, ova attached to mesenteries. 

 Fig. 4. Supposed young ova attached to mesentery: a, muscle retractor 



attached to mesentery ; b, small black dot supposed to be germinal 



vesicle of young ova; c, point of attachment to lower edge of oe,soph- 



agus. 

 Fig. 5. Cluster of ova shovjing attachment : a, lining of calicle; b, mesentery 



in cross section; c, c, c, epiblast ; d, d, d, hypoblast; e, e, pedicels. 

 Fkj. 6. Portion of mesentery belovj gullet shoxving histological structure : a, 



layer of nucleated muscle fibers; b, mesodermal cells; c, layer of 



endodermal cells. 

 Fk;. 7. Portion of axis cylinder: a, semi-calcareous portion showing the 



undulatory course of vermiform bodies; b, corneous central part of 



axis. 

 Fig. 8. A si?igle vermiform body froin semi-calcareous part oj axis cylinder : a, 



fibrous sheath or investment; b, central calcareous deposit showing 



superimposed lamellae. 

 Fig. 9. Transverse section of axis cylinder, greatly magnified : a, corneous part 



or core; b, section of vermiform bodies; c, section of young branch 



from axis. 

 Fig. 10. Section of single vermiform body [more highly magnified): a, sheath; 



b, central calcareous deposit with indications of laminated structure. 

 Figs. II, 15. ^uadri-partite tuberculate spicules. 

 Fig. 12. Simple or double-conic spicule. 



Fig. 13 



Fig. 14 



ViG. 16 



Fig. 17 



Tri partite tuberculate spicule. 

 Papillioform tuberculate spicule. 

 Terete tuberculate spicule. 



Cross-section of partly decalcified spicule shozving concentric lamellate 

 structure. 



