630 



INVEBTEBBATE MOBPHOLOaT. 



separating, rise through the thick test of the parent (Fig. 287, 

 0) until they reach the surface, and develop to complete in- 

 dividuals, in which the process may be repeated. Amarcedum 

 thus forms massive colonies consisting of a number of quite 

 separate individuals all imbedded in a common test, and all 

 directly or indirectly the result of the budding of a single in- 

 dividual developed by the sexual method. 



In other forms, however, the stolon is practically sup- 

 pressed and the buds arise directly from the body of the 



b 



Fig. 288, — A System of Six Individuals from a Compound Colony of 



Botryllv^ (after Oka). 

 a = adult individual. ecp = ectodermal processes extending 



6 = bud. into test from each individual. 



cl = common cloaca. m = mouth of one of the individuals. 



parent. This is the case in Didemnum and Tridemnum, for 

 instance, peculiar complications being also introduced into 

 the process. In the latter form the daughter individual arises 

 as two buds which later fuse. One arises from the upper end 

 of the oesophagus and gives rise to the intestine and neigh- 

 boring organs in the bud, while the other, arising from the 

 branchial sac, gives rise to that structure, the atrium, and 

 terminal portion of intestine. Usually the two buds arise 

 simultaneously, but occasionally one may fail, the result be- 

 ing the production of half individuals which remain united 

 with the parent, producing double monsters ; and since either 



