52G 



THE FUR SEALl^ OF THE PRIBILOF ISLANDS. 



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

 colored than tlie deei)er portions. Sand grains scattered over the surface and also 

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



Zonids. — Closely crowded, particularly in the larger colonies, (piite distinctlj' 

 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 — G, 8, 

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

 off from one another. Length of thorax 3 mm., length of abdomen 3 mm., of post- 

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

 -2r 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 si])lion. 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 (piite distinct and regular lobes. Atrial siphon 

 with abroad dorsal languet, usually two-lobed, but sometimes 

 three-lobed. This htnguc^t very variable in length, in some 

 zooids the siphon dei)arting 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 dilliculty when the anterior end is exam- 

 ined after having been cut off. Tentacles ai)parently 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 ])resent in some individuals, but apparently twelve 

 or thirteen in others — possibly immature ones. Interserial 

 muscle baiuls present; posterior end of the endostyle invari- 

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

 IHgvstire tract. — (Esophagus issuing from 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, wliich lu'ver 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. 



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