60 VERTEBRATE ZOOLOGY 



generalized and the Larvacea as degenerate or paedogenetic, that 

 we have arranged the orders of Urochordata as follows: 



Order I. Ascidiacea (Ascidians). 



Sub-Order 1. Ascidise Simplices. 

 Sub-Order 2. Ascidise Composite 

 Sub-Order 3. Ascidiss Lucise. 



Order II. Thaliacea (Salpians). 



Sub-Order 1. Cyclomyaria (e.g. Doliolum). 

 Sub-Order 2. Hemimyaria (e.g. Salpa). 



Order III. Larvacea (Appendicularians). 



SUB-PHYLUM III. HEMICHORDATA 



The status of this group in the chordate phylum is at best very 

 insecure. While the Enteropneusta, as exemplified by Balanoglossus, 

 seem, on account of certain resemblances to Amphioxus, to have some 

 rather well-founded claims to vertebrate relationship, the Pterobran- 

 chia and Phoronidia are admitted to the phylum Chordata largely by 

 virtue of the almost unmistakable affinities of Cephalodisus with 

 Balanoglossus, and of Phoronis with Cephalodiscus. Without Balan- 

 oglossus, it is unlikely that Cephalodiscus would be considered as a 

 chordate, and without Cephaldiscus, there would be little to connect 

 Phoronis with this phylum. 



ORDER I. ENTEROPNEUSTA 



These are worm-like, burrowing forms with numerous paired gill- 

 slits; intestine running straight from mouth to terminal anus. There 

 are three main body divisions: anterior proboscis; ring-shaped collar; 

 and segmQuied.tr unk, resembling the body of an annelid worm. They 

 are of moderate size, ranging from one inch to four feet in length. The 

 burrowing habits of Balanoglossus (Fig. 33) reveal the significance of 

 these structural peculiarities. Spengel and Hitter have described 

 these in some detail. The proboscis (Fig. 34), which is capable of be- 

 coming swollen or turgid by taking in water through the collar pore, 

 is pushed forcibly against the sand much like the pig's snout in "root- 

 ^ V Sand is loosened and pushed aside until a hole is made deep 

 1 T-h for the proboscis to bury itself. Then the collar, by filling it- 



