ACTINOZOA. 



227 



chamber* appears first, surpassing in size those which follow it. The 

 opposite (posterior) unpaired tentacle and the other paired tentacles 

 then make their first appearance as small wart-like prominences. 

 When the twelve tentacles have been formed, they become alter- 

 nately equalised, so that six larger tentacle*, 

 amongst which are reckoned the unpaired ten- 

 tacles of the long axis, alternate with the same 

 number of smaller ones, and we have two circles 

 of six tentacles of the first and the same number 

 of the second order. 



The asexual reproduction by gemmation and 

 fission is of great significance. Buds can be 

 formed in various positions, even at the oral 

 end, in which case a strobila-like form appears. 

 In Blastotrochus the buds appear at right 

 angles to the axis of the parent animal (fig. 

 171). 

 If the individuals so produced remain connected with one another, 



a polyp-stock is formed, which may attain very various forms and 



great size. As a rule the individuals are imbedded in a common 



body mass, the ccenenchym, and their gastric cavities communicate 



more or less directly, so that 



the juices acquired in the in- 

 dividual polyps penetrate into 



the collective stock. This stock 



affords us an excellent example 



of an animal community built 



up out of similar members. 



The formation of the generative 



products alone is distributed, as 



a -rule, to different individuals, 



which, however, unite in dis- 



FIG. 171. Blattntrochut 

 nutrij; (after C. Sem- 

 per). Z-fiT, Lateral bud. 



charging all animal and 

 together 



vcge- 



(fi* 



t alive functions 

 172). 



The skeletal formations of the FIG. 172. Branch of a Polyparium of CoraUium 

 l ii J.T r rulrum (after L;cazc Duthiers). P, Polyp 



polyps are specially worthy of 



remark (polyparia). In almost every case, with the exception of Ac- 

 tinia, there is a deposit of solid calcareous matter in the mesoclerm, and 



* Like the first tentacle of the young Scyphistoma polyp among the Hydro- 

 Afedusee. 



