TYPE PMOTOGHORDATA. 627 



later fusing to form the extensive atrium. The endostjle (em) 

 is very short, and the nervous system is constructed upon the 

 larval plan, though the brain {g) is not the sensory sac so 

 characteristic of the larva. It is more ganglionlike and sends 

 off branches to an otocyst lying in its neighborhood, and also 

 gives rise to a tubular prolongation opening into the terminal 

 portion of the branchial sac. Pigment-spots, probably rep- 

 resenting rudimentary eyes, are also present, and from the 

 posterior end of the brain a tubular nerve-cord arises which 

 passes backwards and downwards into the tail, which it trav- 

 erses, dilating at intervals into ganglia {g'). The notochord 

 (c) lies below the caudal nervous system, and the lateral 

 muscles of the tail show indications of metameric segmen- 

 tation, 



2. Order Ascidiacese. 



The members of this order present the structural features 

 which have been described as typical for the class. Many 

 forms possess the power of non-sexual reproduction by bud- 

 ding, colonies being thus produced some of which may be 

 free-swimming, the simple forms, however, being always fixed. 

 They differ from the Larvacese chiefly in the absence of the 

 tail in the adult and in the large development of the branchial 

 sac and the numerous stigmata. 



Owing to the complexities produced by the methods of 

 budding it is customary to divide the order into subordinate 

 groups. 



1. Suborder Ascidim simplices. 



The simple Ascidians agree with the description given as 

 typical and do not require any further notice here, except to 

 mention the fact that there are included within the suborder 

 a few genera which reproduce by budding, e.g. Clavellina and 

 PeropJiora. The formation of new individuals takes place in 

 these cases from stolonlike outgrowths of the parent form, 

 and each bud remains seated upon the stolon surrounded by 

 its own test. The stolon (Fig. 286) arises from the lower por- 

 tion of the body of the parent and pushes before it a portion 



