ACTINOZOA. 



227 



FIG. m.Blaatotrockus 

 n/itrix (after C. Sem- 

 per). LK, Lateral bud. 



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 tentacles, 

 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 BlastotrocJius 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- 

 charging all animal and vege- 

 tative functions together (fig. 

 172). 



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



polyps are specially worthy of rulr>u " (after Lacaze Du ^ers). P, Polyp, 

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

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



Like the first tentacle of the young Scyphtstoma polyp among the Hytl ro- 

 Medusee. 



