IV 



INTRODUCTION. 



Stolon. — The creeping tubular stem, by which the 

 individual zooecia or celliferous shoots composing a colony- 

 are held together, in certain members of the class (e. g. 

 the Ctenostomata) . 



General plan or Structure. 



In every polyzoon we distinguish two fundamental 

 elements, the zooecium and the polypide. These are the 



Fig. i. 



S. Membranous sac. t. Tentacular crown. o. Mouth. as. (Eso- 

 phagus. st. Stomach, int. Intestine, a. Anus. y. Nervous 

 ganglion. /. Funiculus, ov. Ovary, sp. Spermary. 



primary zooids in every colony. When the larva fixes 

 itself, after its brief term of free life, it is metamorphosed 



cell of Crida and other forms, and the superficial inflation of the zoarium 

 in which the embryos are developed in many of the Cychsfomata. It is 

 clearly desirable, however, that these very different structures should be 

 distinguished by separate names. 



