522 



THE FUR SEALS OP THE PRIBILOF ISLANDS. 



ei... 



opaque with the contained generative and mesenchyme cells. It gradually narrows 

 toward its attachment to the abdomen, but is not pedunculated, it being at the junction 

 fuUy as thick as the abdomen itself. 



Mantle. — Very thin, though its ectodermal layer presents, particularly 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 mautle. 



Branchial apparatus. — 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 elongated, 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 the atrial orifice 

 (fig. 20). Owing to the persistently contracted condition of the 

 anterior portion of the branchial sac the number and arrange- 

 ment 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 stigmata. 

 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 posterior side. 

 Digestive tract.~(Esop]\agiis about equaling the stomach in length, stomach 

 somewhat longer than broad when not contracted, extension of loop behind stomach 

 about equal to the combined length of the oesophagus and stomach; rectal portion of 

 intestine passing to left of the oesophagus to reach the mid dorsal line in the region 

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

 no well-defined folds. 



Sexual organs.— Gonads contained in the large post-abdomen, the testis consisting 

 of a large number of closely crowded lobes, occupying its posterior two-thirds, while 

 the ovary is confined to its narrower anterior third. The ovary is situated close 

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

 sometimes on the right and sometimes on the left of the loop of the intestine. No 

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



This species, which I take pleasure iu dedicating to President Jordan, belongs to 

 a group of Ascidians, the exact systematic position of wliich has troubled me for some 



