INTRODUCTION. lxxxv 



Order 3. 

 PODACTINARIA. 



Polypi having the gastric cavity surrounded by four vertical membranaceous septa, at 

 the upper end of which are placed four pairs of intestiniform reproductive organs. The 

 tentacula discoidal, pedunculated, not tubular as in Zoantharia and Alcyonaria, but 

 organized much in the same way as in Echinoderma. The mouth proboscidiform, and 

 the fauces surrounded by numerous internal, filiform, contractile appendices. 



The genus Ldcernaria is the only known representative of this zoological type, and 

 comprises no coralligcnous polypi. 



Sub-class 2. 

 HYDRARIA. 



Polypes sertulariens, Audouin and Milne Edwards, Recherches sur les Anim . sans Verteb., faites aux iles 

 Chausay, in Ann. des Sc. Nat., 1st series, vol. xv, p. 18, 1828, ap. Lamarck, Hist, des An. sans Verteb. 

 2d ed., vol. ii., p. 10.3; Sertulariacaa (in parte), Blainville, Manuel d'Actinologie, p. 4G."), 1834; 

 Zoocorallia olig actinia, Ebrenberg, Coral. Roth. Meeres, p. 67, 1834; Zoophjta Hydroida, Jobnston, in 

 Mag. of Zool. and Bot., vol. i, p. 44", 1837; Polyparia, Gray, Synop. Brit. Mus. ; Nudibranehiata, Farre, 

 on tbe Structure of Polypi, Phil. Trans. 1837; Hydrozoa, R. Owen, Lectures on the Conip. Anat. of the 

 Inverteb. Animals, p. 82, 1843; Hydroidea, Dana, Exploring Expedition, Zooph. p. GS5, 1846; 

 Anthozoa Hydroidea, Johnston, British Zooph, 2d ed. p. 5, 1847. 



Polypi with a simple, non-lamelliferous, digestive cavity. No internal generative 

 organs. Tentacula filiform and subverrucose. 



The naked, fresh-water zoophytes of the genus Hydra constitute the type of this 

 group, and till very lately were considered as being closely allied to Sertularia, Campanu- 

 laria, &c. ; but the recent observations of divers zoologists tend to establish that all the 

 coralligenous animals of this form belong to the class of Medusa. Till this question is 

 decided, it would therefore be idle to make any modifications in the systematic arrange- 

 ment of these problematic polypi, and it will suffice for us to refer the reader to Dr. 

 Johnston's valuable work on ' British Zoophytes,' for the characters of the generic 

 divisions generally adopted. 



