227 



FIG. 17l^-Bla*totroc?Mt 

 nutrix (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 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- 

 charging all animal and vege- 

 tative functions together (fig. 

 172). 



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



rubrum (after Lacaze Dllthiers )- p > 





polyps are specially worthy of 



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



tinia, there is a deposit of solid calcareous matier in the rnesoderm, and 



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

 Mcdusce. 



