168 CHORDATA. 



of the circulation, and the frequent reversal of its direction, can 

 be observed. 



3. From the dorsal end of the heart a cardio-visceral vessel 

 runs to the visceral mass, where it divides into smaller vessels. 

 These, reuniting, form the viscero-branchial vessel which extends 

 along the dorsal surface of the pharynx above the dorsal lamina. 

 Numerous small branchial vessels in the pharyngeal wall connect 

 this vessel with the branchio-cardiac, which lies ventral to the 

 endostyle and unites with the ventral end of the heart. The 

 frequent reversal of the current can be readily seen both in the 

 heart and in the vessels. 



The relation of the parts will be more clearly understood if 

 a second large specimen is dissected as follows: With scissors 

 cut off the atrial siphon, thus exposing the atrium; then simi- 

 larly remove by a single cut the oral siphon, together with the 

 anterior end of the pharynx (the piece thus cut off should contain 

 the ganglion, dorsal tubercle, peri-pharyngeal bands, oral tentacles, 

 anterior portion of the endostyle, dorsal lamina, etc.). 



Make drawings that will show the structure. 



PEROPHORA. 



This colonial simple ascidian occurs on piles and other sub- 

 merged materials, and is commonly attached by branching 

 stolons to seaweeds, simple tunicates, or other sessile animals. 

 Material should be quite fresh for satisfactory study, and should 

 be carefully handled to avoid crushing. Study in a watch-glass 

 of sea-water (or support the cover-glass), with a low power of the 

 microscope. 



1. Notice that the individuals are essentially very much like 

 miniature Molgulas. Identify as many of the organs that were 

 seen in Molgula as possible, noting the differences. 



2. The form illustrates the type (Clavelinidai) in which a 

 colony is formed by budding from a stolon, but in which the 

 individuals retain their identity to a great degree and have sepa- 

 rate tunics. 



