3o8 CHORD AT A. 



ventral parts unite together to form the continuous coelom and the 

 dorsal parts divide into three portions, the sclerotome, myotome and 

 gonotome, which give rise to the connective tissue, myomere muscles 

 and the gonads respectively. 



The larva lives for about three months in pelagic water and then moves 

 to the sandy bottom. During this period the rows of pharyngeal clefts 

 appear as paired apertures, and the atrium arises as a mid-ventral 

 ingrowth of epiblast which pushes the coelom before it and comes to lie 

 around the pharynx. It will be noticed that up to the production of the 

 chordula larva the development is closely similar to that of Ascidia. 



