350 THE AUSTRALIAN HYDROMEDUS^E, 



4. FAMILY EUDENDRID^E. Allman, 1872. 



The alimentary Zooids possess one verticil of filiform tentacles, 

 and mature the generative elements on tentacular appendages. 



During the maturing of the sexual products the sexual zooids 

 often become rudimentary and loose their tentacles. 



3. GENUS EUDENDRIUM. Ehrenberg. 



Every Polypostyl is actually a rudimentary Polyp, and the 

 generative elements make their appearance before tentacles and 

 mouth become rudimentary. This latter does not always take 

 place, and then the mature generative elements are found partly 

 on Polypostyls and partly on ordinary Polys. The colonies 

 consist of an anostomising Hydrorhiza from which branched stems 

 arise. The structure of Eudendrium has been investigated 

 particularly by Weismann (1.) Jikeli (2), and myself (3.) 



The Ectoderm, and particularly the Entoderm, are very much 

 higher developed than in Hydra. We meet with separate 

 epithelial and sub-epithelial layers. The Ectoderm consists of a 

 superficial layer of covering, sensitive and glandular elements, and 

 cnidoblasts of two different kinds, and the sub-epithelial cells. In 

 a ring around the base of the Hydranth gland-cells of a peculiar 

 kind, are amassed on the two sides of a deep groove which 

 surrounds the Polyp. Below these elements we met with longi- 

 tudinal muscles, with ganglia cells, and with a few indifferent 

 insterstitial cells. 



The Entoderm also consists of more layers than one. Super- 

 ficially we find ciliated cylindrical cells and gland-cells of various 

 kinds. The sub-epithelial layer below these is particularly highly 

 developed in the proboscis, and contains in that region ganglia 

 cells and circular muscles, the cells of which are intra-epithelial. 



(1.) A. Weismann. Die Entslehunq der Sexual:< /< n In i d n Hydromedvst n. 

 Seite, 91, 109. 



(2.) C. Jikeli. Der Ban der Hydroidpolypenl. Morphologisches Jahrbuch. 

 Band, VIII. Seite, 376, 391. 



(3.) II. von Lendenfeld. Das Nervensystem der Hydroidpolypen, Zoolo- 

 gischer Anzeiger. Band, VI. Seite, 69. 



