INVERTEBRATE AXIMALS OF VINEYARD SOUND, ETC. 389 



tirely imbedded in the gelatinous mass that unites them together. They 

 are arranged in circular, oval, or stellate groups, with a common cloacal 

 orifice in the center of each cluster. The masses are usually pale orange- 

 red, varying to yellowish and pale flesh-color. The stomach of each in- 

 dividual is bright orange-red j the branchial sac is flesh-color, pale yel- 

 low, or orange ; the tubes and upper part of the mantle bright orange or 

 lemon-yellow. 



The Botrijllus Gouldii (p. 375, Plate XXXIII, figs. 252, 253) also fre- 

 quently' occurs on the piles of the wharves, creeping over the stems of 

 Tubularians, the surfaces of other ascidians, fronds of algie, or on the 

 surface of the wood itself. It also frequently forms broad, soft incrusta- 

 tions on the bottoms of boats, floating timber, &c. 



The Bryozoa are also usually quite abundant on the piles and timbers 

 of wharves, &c. 



The Bugida ^Jtrrifa (p. 311, Plate XXXIY, figs. 258, 259) is one of the 

 most common as well as one of the most elegant of these. It occurs at- 

 tached to the adhering sea-weeds, &c., forming delicate white plumes. 



The Escliarella variahilis (p. 311, Plate XXXIII, fig. 256) usually forms 

 firm, coral-like incrustations, but when attached to hydroids and sea- 

 weeds it spreads out into foliaceous or lichen-like, rigid, calcareous 

 fronds, which are dull red while living. 



On the piles at Wood's Hole the Bugula flahellata was also very abun- 

 dant. This forms elegant circular or fan-shaped fronds, consisting of 

 numerous repeatedly forked, flat, and rather narrow branches, on which 

 the cells are arranged iu about three longitudinal rows. This species, 

 like others of the genus, bears verj^ singular structures, known as avicu- 

 laria, which, under the microscope, have the form and appearance of the 

 stout, hooked beaks of certain birds, such as the hawk, owl, parrot, 

 &c. These beaks are attached by flexible stems, and are provided in- 

 ternally with powerful muscles by means of which they are constantly 

 opened and closed, and can bite with considerable force. In this 

 species these are attached to the sides of the cells, along the edges 

 of the branches. Their office seems to be to defend the colony against 

 small parasites, and dirt of all kinds, which, unless thus removed, would 

 soon cover up the cells and destroy the animals. In addition to these, 

 various less conspicifoas species often occur in abundance, especially 

 Yesicularia gracilis ; V. clichotoma Y. ; and Y. cuscuta. 



Of Radiata there are but few species iu such localities, with the excep- 

 tion of the Hydroids, which are usually very abundant. 



The green star-fish, Xs-^erirts arenicola, (p. 3 JO, Plate XXXY, fig. 269,) 

 may occasionally occur adhering to the piles just below low- water mark, 

 but it does not have this habit to such an extent as does the A. vulgaris, 

 north of Cape Cod, for the latter is almost always to be seen in abun- 

 dance on the piles of the wharves of the northern seaports, as at Port- 

 land, Eastport, &c., and less abundantly at Boston. 



One of the most beautiful, as well as one of the most abundant, of 



