Structure of the Campanularise, Sertuldinx, and Hydridse. 55 



sions, of which that introduced between the mouth-piece and 

 the stomach may be called the " oesophageal passage " (Schlund- 

 enge), and that between the stomach and transition-piece, in 

 the orifice of the so-called diaphragm, the '^portal passage" 

 (Pfortnerenge). In many genera belonging to this group the 

 stalk bears the secondary heads *, particularly characterized by 

 their urticating organs, most frequently in the vicinity of the 

 polype-heads, apparently as appendages of the latter, 



4. In the Hydrida the stomach passes, without any distinctly 

 limited transition-piece, into the polype-stem or foot ; the 

 *' portal passage " also is not marked externally, but may be 

 recognized during the closure of the stomachal cavity from that 

 of the foot. The Hydridce are further distinguished from the 

 Campanularii2 and Sertularice by the fact that the former are 

 naked and possess no polyparium, and particularly by the struc- 

 ture of the tentacles. 



5. The Campanulari(Bj Sertularice, and Hydridce are ad- 

 mitted on all hands to consist in all their parts, excepting 

 the arms, of two chief constituents or layers, the ectoderm 

 and endoderm of AUman. Between these two principal layers 

 a third accessory constituent, named by me the "supporting 

 lamella^' or "supporting membrane," a sort of inner skeleton, 

 is everywhere introduced. This has already been conjecturally 

 established by Leydig and KoUiker {basement membrane). All- 

 man has regarded the supporting lamella as a muscular fibrous 

 layer. 



6. In the developed state the ectoderm does not consist of 

 cells j it is not an epithelium as is generally supposed, but is 

 the essential and sole contractile substance of the polypes, com- 

 parable to that of the Polythalamia ; it contains imbedded in it 

 the urticating organs and sometimes also pigment-corpuscles, 

 but otherwise not the least trace of nuclei or of any cell-consti- 

 tuent. The contractile substance itself is perfectly transparent 

 and of perfectly uniform homogeneous texture, as in the Poly- 

 thalamia. It acquires the aspect of a cellular structure only 

 during certain states of contraction, especially the papillar 

 condition. 



7. During the transition of the cortical layer from the state 

 of rest to that of so-called active contraction, there appear upon 

 any part of its outer surface small knots, warts, papilliform pro- 

 jections, and ridges of variable number and size. The ridges 

 are regularly transverse in direction, embracing the cavity more 

 or less completely. Such annular ridges are formed, however, 

 only on the very mobile parts of the body, but therefore all over 

 the Hydrida. In Hydra the head and foot may in this way ac- 

 quire a very regularly ringed appearance. The papillie of con- 



* Nematophores of Busk. 



