102 



COELENTERATA. 



FIG. 83. Axial 

 cells from the 

 tentacles of 

 Campanularia. 



As a rule there is no localised organ for the excretion of the 

 nitrogenous waste, but in a few cases deposits of guanin or urea crystals 

 may be seen in some of the endoderm cells. Some 

 polyps possess pores at the apices of the tentacles or 

 through the body wall, which may serve for excretion 

 (Fig. 84). 



Asexual reproduction by budding or fission is very 

 commonly found. If the individuals so produced 

 remain united they give rise to the colonies which 

 are so widely distributed amongst the Cnidama, and 

 which by the continued multiplication of their mem- 

 bers may attain a considerable size. 



Sexual reproduction is always met with. The 

 sexual cells arise in the endoderm or ectoderm. They 

 sometimes remain at their place of origin (Hydra, Anthozoa), but 

 often they pass through the supporting lamella and wander to 

 ea> , another place where they 



ripen (most Hydromedusae). 

 There are two kinds of 

 polyps, characterised by the 

 structure of the enteric cavity 

 the Hydroid polyp and the 

 Antliozoan or coral polyp. 

 As types of the former we 

 may mention Hydra with 

 ^ s s i n gl e row f hollow 

 tentacles, and Tubularia 

 with its double row of solid 

 tentacles. In such polyps 

 the gastrovascular space is 

 simple, and there is no 

 oesophageal tube. 



The Antliozoan Polyps 

 are usually of a larger size 



,-, ,, * TT i i i 



tnan tlie JlydrOldS, and 



c. 



FIG 84. Diagrammatic longitudinal section through 

 an Antliozoan polyp, passing through an enteric 



pouch on the left side and through a mesentery possess a more complicated 

 on the right, e perforation in mesentery ; elc ecto- ' 

 derm; en endoderm (black); ex excretion -pores 

 (cinclides); ex' excretion pore at the end of a 

 tentacle ; /pedal disc ; g.t. enteric pouch ; m wall 

 of body ; mes supporting lamella ; mf mesenterial 

 filament; o mouth; oes oesophageal tube ; p edge 

 of penstome ; s supporting lamella of a mesentery ; 



t tentacle (from Chun). 



., ,^. 

 gastrovascular Cavity (.big. 



4) In the first place the 

 mouth leads into a tube 

 ^focll projects into the gas- 



trovascular cavity, and opens 



