526 



THE FUR SEALS OF THE PRIBILOF ISLANDS. 



off from one another. 



particularly in the larger colonies. A surface layer considerably denser and darker 

 colored than the deeper portions. Sand grains scattered over the surface and also 

 penetrating the whole test mass. Cells numerous in the test, but no vessels. 



Zooids. — Closely crowded, particularly in the larger colonies, quite distinctly 

 visible on the surface of the colony, each standing generally at nearly a right angle to 

 the surface. Systems usually distinct, number of zooids in each usually small — 6, 8, 

 or 10, sometimes more. The three divisions of the body distinct, but not constricted 

 Length of thorax 3 mm., length of abdomen 3 mm., of post- 

 abdomen 5 to 10 mm., depending on the extent of develop- 

 ment of the testis. 



Post-abdomen when fully developed somewhat, though 

 not greatly, larger at its posterior than at its anterior end. 

 (Fig. 25.) 



Mantle. — Feebly developed. Circular muscle fibers almost 

 wholly absent, they being restricted to a few scattering ones 

 around the branchial siphon. Longitudinal fibers grouped in 

 distinct bundles, though these not numerous. 



Branchial apparatus. — Branchial orifices easily recogniz- 

 able on the surface of the colony by the aid of hand lens, 

 though no lobes visible. Common atrial orifices moderately 

 large. When removed from the test, branchial siphon found 

 to possess six quite distinct and regular lobes. Atrial siphon 

 with a broad dorsal languet, usually two-lobed, but sometimes 

 three-lobed. This languet very variable in length, in some 

 zooids the siphon departing but slightly from the normal six- 

 lobed condition. 



Anterior half of the branchial sac usually considerably 

 more contracted than the posterior half. The globular gan- 

 glion seen without difficulty when the anterior end is exam- 

 ined after having been cut off. Tentacles apparently about 

 twenty in number, of different lengths, about half of them 

 being long and stout. The circle situated close to the siphon. 

 Branchial sac well developed. Fifteen series of stigmata 

 certainly present in some individuals, but apparently twelve 

 or thirteen in others — possibly immature ones. Interserial 

 muscle bands present; posterior end of the endostyle invari- 

 ably produced into a U-shaped loop in the preserved specimens. 

 Digestive tract. — CEsophagus issuing irom the postero- 

 dorsal angle of the branchial sac; form and proportions of 

 the tract as a whole conforming closely to the usual type for 

 the genus. Stomach somewhat barrel shaped, folded longitudinally, but the folds are 

 irregular and are neither conspicuous nor numerous, the number being about seven. 

 In addition to the folds, or rather furrows, which never involve the entire surface, 

 there is a tendency for the surface between the furrows to become areolated in many 

 specimens. (Fig. 25.) 



Sexual organs. — Ovary immediately behind and in contact with the intestinal loop, 

 small in volume as compared with the testis, which latter is very large, it appearing 

 to constitute almost the whole of the long post-abdomen. ^ 



