PACIFIC TUNICATA OF U.S. NATIONAL MUSEUM 55 



hypoabdominal layer near the bottom. Test sometimes irregularly 

 thickened at random on surface. Zooicls transparent and pinkish or 

 quite colorless in preserved specimens. Thoraces situated perpen- 

 dicularly, while abdomens are placed obliquely. Abdomens one-half 

 to two-thirds the length of thoraces; postabdomon mostly as long as 

 abdomen. Thorax about 2.5 mm. in length in zooids examined in the 

 colony from Japan, whereas in some zooids of the colony from the 

 Palau Islands it reaches 5 mm. and abdomen attains 2 mm. System 

 of zooid arrangement obscure in all specimens, because entire surface 

 is encrusted with sand grains. Branchial aperture 6-lobed and atrial 

 aperture situated at level of the first to fourth stigmatal row. Atrial 

 languet very long, its tip simple, trifid or bluntly truncated and with 

 several small prominences as shown in figure 16c. A small promi- 

 nence may be found on dorsomedian line just posterior to atrial aper- 

 ture. Up to a dozen longitudinal muscles on each side of thorax, of 

 which 6 to 10 ventral ones are rather thick, whereas the dorsal ones are 

 somewhat delicate. Stigmatal rows 14 to 18, usually 15; generally 15 

 to 20 stigmata in each row, although as many as 40 in some zooids of 

 the colony from the Palau Islands. Papillae on the horizontal mem- 

 branes very distinct, usually arranged one to each one or two stigmata. 

 Tentacles 16 to 24 in the zooids examined, larger and smaller ones 

 alternating regularly. Ciliated groove a small elliptical opening. 

 Dorsal languets situated along dorsomedian line or in some zooids 

 somewhat displaced from midline to left side for distance of 4 stigmata. 

 Anus bilobed and opening at level of seventh or eighth transverse ves- 

 sel, except at level of the thirteenth transverse vessel in zooids having 

 17-18 stigmatal rows. Three to seven fertilized eggs or embryos in 

 various developmental stages found in incubatory pouch. Surface of 

 stomach smooth. Proximal portion of rectum somewhat swollen, 

 forming a pair of small caeca in some zooids; outer side of this swollen 

 portion sometimes cut faintly into 5 lobules (fig. 15d). Rectal wall in 

 region between level of the cardiac end of stomach and middle constric- 

 tion of hind stomach surrounded by whitish circumintestinal glands. 

 Ovary usually situated at the center of testis, but anterior to testis in 

 some zooids. Testicular follicles generally 15-31, although in zooids 

 of the colony from the Palau Islands there are only four and all very 

 small. Posterior part of postabdomen, containing pericardium, occu- 

 pies one-third to two-thirds of postabdomen. 



Larvae elliptical in shape and from 460 to 520/x in length. Four 

 pairs of low ampullae present. Three cup-shaped attachment proc- 

 esses arranged lineally; oval in outline on the surface. Four pairs of 

 small vesicles found at posteroventral part of trunk in embryos from 

 the Japanese colony. Sensory organ situated at the level of posterior 

 one-fourth to one-third of the trank; two pigment flecks arranged 

 anteroposteriorly (fig. 16^). 



