Introduction to Animal Morphology. 79 



flagellate nuclei of modified endodermal (?) cells. The forms 

 included herein are singularly plastic, easily modified by ex- 

 ternal conditions. The group with inconstant, simple, 

 dermal pores constitutes the sub-order Ascones.*' The series 

 "with tortuous branched canals in the wall of the gastrseal 

 •cavity are named Leucones, while those with regular, straight, 

 unbranched vessels and budding tubes are Sycones ; any of 

 these may possess either simple or three- or four-rayed 

 spicules, or two or more kinds together, and by these Haeckel 

 divides them into genera. The flagellate plastides of 

 Leucosolenia (Ascones) have been regarded by James-Clark 

 as separate organisms grouped in a colony (see Synura). 



CHAPTER XII. 



SUB-KINGDOM 3. — CCELENTERATAf [Leuckart). 



Aquatic radiated personae (often in colonies) of more 

 than two antimeres, having a body cavity opening at 

 one pole by a mouth often surrounded by feelers 

 (tentacles). The body consists of two membranes, an 

 inner, cellular or endoderm, which at the mouth joins 

 the outer, or ectoderm. In the colonial forms, the 

 tubular prolongation of the body cavity of each 

 persona communicates with that of its neighbours in 

 the common stem of the colony (Coenosarc), allowing 

 of community of nutrition, and the fluid, produced by 

 digestion in the stomach of each, circulates in this 

 tubular system, moved by the lining cilia. Dif- 

 ferentiations of the ectoderm form support-, loco- 



* These are the simplest known gastnilse. 



t Diploblastica {Lankester), called so in contrast \vith the Ablastica 

 ((Protozoa), and Triploblastica, including aU the other Metazoa. 



