522 



THE FUK SEALS OF THE PRIBILOF ISLANDS. 



ei.... 



opaque with the coutaiued geueiative aud mesenchyme cells. It gradually narrows 

 toward its attachment to the abdomen, but is uot pedunculated, it being at the juuctiou 

 fully as thick as the abdomen itself. 



Mantle. — Very thin, though its ectodermal layer presents, ijarticularly in posterior 

 part of the post-abdomen, a layer of well-defined epitheloid cells. Musculature con- 

 sisting of a few small, widely separated bundles of longitudinal fibers and a still 

 .smaller number of circular fibers, the latter confined to the anterior region of the 

 animal. Owing to this disposition of the circular fibers, in the contracted state the 

 anterior end of the thorax becomes much smaller and denser than the posterior end. 

 But few mesenchyme cells in the njautle. 



Jiranchial apimratus. — Branchial orifices readily seen on the surface of the colony 

 by the aid of a hand lens, but the atrial orifices scarcely visible; former circular in 

 outline, no lobes distinguishable till the zooids are removed from tlie test, when the 

 branchial siphon is found to be obscurely six lobed, while the atrial siphon, often 

 considerably elongattd, has no constant lobulation. In some 

 zooids a large lobe, undoubtedly representing the atrial languet 

 of some species, is seen on the dorsal side of tlie atrial orifice 

 (fig. 20). Owing to the i>ersistently contracted condition of the 

 anterior i)ortion of the l)ranchial sac the number and arrange 

 inent of the branchial tentacles have not been determined; it 

 is, however, found that they are rather small and few in num- 

 ber. Peripharyngeal band situated close to the branchial 

 siphon. Ganglion not large, spherical, distinctly seen through 

 the mantle in uncontracted zooids. Hypophyseal duct distinct, 

 wide mouthed, well ciliated. Endostyle of moderate size, never 

 greatly tortuous, extends forward nearly to the base of the 

 branchial siphon. Branchial sac well developed, 12 or 13 series 

 of stigmata, each half series containing about 15 stignuita. 

 Well developed interserial muscle bundles. Dorsal languets at 

 least as numerous as the series of stigmata.; highly developed, 

 sickle shaped, with the concave side directed forward, the 

 epitheloid cells of the wall of this side (considerably higher 

 than those of the convex or ])osterior side. 

 IHffestive tract. — (Esopliagus about equaling the stomach in length, stomach 

 somewhat longer than broad when not contracted, extension of loo}) behind stomach 

 abcmt ecjual to the combined length of the (esophagus and stomach; rectal i^ortion of 

 intestine passing to left of the (esophagus to rea(!h the mid dorsal litie in the region 

 of the branchial sac. Stomach wall with a few irregular longitudinal thickenings, but 

 no well-defined folds. 



Sexual onfans. — Gonads contained in the large jmstabdomen, the testis consisting 

 of a large nund)er of closely crowded lobes, occui)ying its posterior two-tliirds, wiiile 

 the ovary is confined to its narrower antc^rior third. The ovary is situated close 

 behind the intestinal looj). Vas deferens, well filled with ripe sperm, passes forward, 

 sometimes on the right and sometimes on the left of the looj) of tiie intestine. No 

 embryos or ripe ova in the specimens at hand. No buds seen. 



This species, whicii I take i)leasure in dedicating to President Jordan, belongs to 

 a grouj) of Ascidiaus, the exact systematic i)ositi()n of wliich has troubled me f(«' some 



