100 THE AMERICAN MONTHLY. [June, 



frightened into their protective cells, they are usually slow to show them- 

 selves again ; but a sight of their graceful plumes is worth waiting for. 



The colonies of tube-forming Polyzoa are visible to the unaided vision as 

 brownish, chitinous, thread-like objects, adherent to the lower surfaces of 

 stones and other submerged substances, for most of them shun the light. 

 These thread-like, often branching, tubules are quite firm to the touch, and 

 they are sometimes dislodged from their support with difficulty. To collect 

 them, it is usually best to take stone and all, or to remove them with a large 

 slice of the wood ; if then placed in a watch-glass, on the stage of the micro- 

 scope, in water of course, the enclosed animals w^ill sooner or later expand 

 their plumes and amply reward the patient watcher. » 



About the only portion of the animal, or polvp, usually extended beyond 

 the cell which it secretes and inhabits, is that part named the lophophore, 

 on which are the long, flexible and peculiarly graceful tentacles. This 

 lophophore may be shaped like a horse-shoe, it may be oval, or circular. 

 The tentacles are always entirely ciliated, and vary greatly in number in the 

 various species. 



Reproduction takes place by budding, and by the formation of statoblasts, 

 or the so-called ' winter eggs.' These are oval, brownish bodies, quite visi- 

 ble to the unaided vision, \vhen seen under favorable circumstances. They 

 are formed in the autumn, leaving the animal only when the latter dies, and 

 the soft body melts awa}- in the water. The softening masses of Pectinatella 

 are often to be found in the fall, densely studded with these reddish-brown 

 statoblasts, the margins of the latter, in this case, being bordered by a row 

 of doubly-barbed hooks. These statoblasts remain unchanged until spring, 

 when each one then produces an embryo, which finally develops into a polyp. 



The following analytical key to the known species of fresh-water Polyzoa 

 is based almost exclusively on Dr. J. Jullien's ' Monographic des Bryozo- 

 aires d'Eau Douce,' originally published in the Bulletin de la Societie Zoolo- 

 gique de France, t. X, 1S85. In this country, the only papers on the subject, 

 easily accessible to the student, are Dr. Leidy's contributions to the Academy 

 of Natural Sciences of Philadelphia, and Prof. A. Hyatt's ' Observations on 

 Polyzoa, Sub-order Phylactola^mata,' where many anatomical details may 

 be found. 



Key to Genera. 



§ Colonies formed of chitinous cells («). 



§ Colonies formed of gelatinous tubular cells {b). 



§ Colonies a jellj-mass surrounding the polyps (c). 

 a. Cells urn-shaped ; lophophore subcircular: colonies pendent, . Uriiafella, i. 



a. Cells tubular ; lophophore horse-shoe shaped, .... Plumaiella, 2. 

 a. Cells tubular ; lophophoi-e circular or oval, ..... Frederi'cclla, t,. 

 a. Cells clavate, growing end to end ; lophophore circular, . . Paludicella, S. 

 a. Cells cordate ; lateral walls thick ; centre thin : colonies linear, prostrate, branching, 



JVorodotiia, 9. 



a. Cells subcircular, flat; sides thick; front thin, transpai-ent ; colonies prostrate, 



usuallj' indefinite, ......... Hislopia^ 10. 



b. Branches not attached ; lophophore horse-shoe shaped, . . . Hyalinella, ^. 



c. Colonies more or less globular, permanently fixed (</). 



c. Colonies oval or elongate, flattened, slowly traveling, . . . Crtstatella, 7. 



d. Colonies sacciform, finally lobed or branched; statoblasts not spinous, 



I^o;pJiopus, 5. 

 d. Colonies globular, orifices grouped in lobed areolie; statoblasts marginally spinous, 



Pectinatella, 6. 



Description of Species. 



I. Urnatella. 



Colonies flexible, |^ to ^ in. long, branching ; cells centrally translucent, 

 pale, brown-lined transversely and spotted, ends black, opaque, a cup-like 



