102 



COELENTERATA. 



FIG. 83. Axial 

 cells from the 

 tentacles of 



". 



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 Cnidaria, 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 



another place where they 

 ripen (most Hydroinedusae). 

 There are two kinds of 

 polyps, characterised by the 

 structure of the enteric cavity 

 the Hydro-id polyp and the 

 Antliozoan or coral polyp. 

 As types of the former we 

 may mention Hydra with 

 its single row of hollow 

 tentacles, and Tulndaria 

 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 



FIG 84. Diagrammatic longitudinal section through fl ,1 TTvrlvrnrl inrl 



,. ,. . . Lllclll lllfc> -11 \ U.1U1U.O. (111U. 



an Antliozoan polyp, passing through an enteric 



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



on the right, r perforation in mesentery ; ek ecto- O . nc ,trov<iscukr cavitv CFi" 



derm; en endoderm (black); ex excretion - pores o ast ' 



(cinclides); c./' excretion pore at the end of a 84). Ill the first place the 



tentacle ; /pedal disc ; <j.i. enteric pouch ; m wall , , -. -, 



of body ; mes supporting lamella ; mf mesenterial niOUtll 



filament; o mouth; ocs oesophageal tube; p edge w hicll projects into the gas- 



of peristome ; s supporting lamella of a mesentery ; 



t tentacle (from Chun). trovascular cavity, and opens 



c. 



