xin PHYLUM CHORDATA 19 



or peribranchial cavity. The principal nerve-ganglion gives off a 

 nerve cord with ganglionic enlargements running to the tail, 

 along the dorsal aspect of which it passes to the extremity. 

 There is no reproduction by budding, and development takes 

 place without metamorphosis. 



This order contains only a single family, the Appendiculariidce, 

 with five genera, including Appendicularia and Oikopleura. 



ORDER 2. THALIACEA. 



Free-swimming Tunicata, sometimes simple, sometimes colonial, 

 never provided with a caudal appendage in the adult condition. 

 The test is a permanent structure. The muscular fibres of the 

 body- wall are arranged in complete or interrupted ring-like bands, 

 or diffusely. The pharynx has either two large or many small 

 stigmata leading into an atrial cavity which communicates with 

 the exterior by the atrial aperture. There is usually an alterna- 

 tion of generations ; there may or may not be a tailed larval 

 stage. 



Sub-Order a. Cydomyaria. 



Thaliacea with a cask- shaped body, having the oral and atrial 

 apertures at opposite ends, and surrounded by a series of complete 

 rings of muscular fibres. 



This sub-order contains only one family, the Doliolidce, with the 

 three genera, Doliolum, Anchinia, and Dolchinia. 



Sub-Order b. Hemimyaria. 



Thaliacea with a more or less fusiform body, with sub-terminal 

 oral and atrial apertures. The muscular fibres are arranged in 

 bands which do not form complete rings. 



There are two families the Salpidce and the Octacnemidce 

 the latter comprising only the aberrant deep-sea genus Octacnermis, 

 which seems to be fixed and not free-swimming like the rest of 

 the order. 



Sub-Order c. Pyrosomata. 



Thaliacea which reproduce by budding, so as to give rise to 

 hollow cylindrical colonies, open at one or both ends, having the 

 zooids embedded in the gelatinous wall in such a manner that the 

 oral apertures open on the outer, the atrial on the inner, surface 

 of the cylinder. 



This sub-order comprises only one family, the Fyrosomidce, with 

 one genus, Pyrosoma. 



ORDER 3. ASCIDIACEA. 



Mostly fixed Tunicata, either simple or forming colonies by a 

 process of budding, and, in the adult condition, never provided 



c 2 



