INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 375 



The Aseidians are generally uncommon on muddy shores, but wherever 

 the eel-grass nourishes, and especially in sheltered situations, the Mqlgula 

 Manhattensis (p. 311, Plate XXXIir, fig. 250) is usually to be found ad- 

 hering to it. The Botrijllus Goiddii (Plate XXXIII, figs. 252, 253) is also 

 frequently found growing upon the eel-grass in such situations, as well 

 as upon the piles of wharves, bottoms of boats, &c. This species was 

 found in great profusion upon the eel-grass in Little Harbor, at Wood's 

 Hole, and in Waquoit Pond. In both these localities the water is nearly 

 pure and but slightly, if at all, brackish. But it has also been found by 

 Professor D. C. Eaton on the piles at Brooklyn, Xew York, where the 

 water is more brackish. This species when young forms thin, soft, circu- 

 lar or oval incrustations covered with stellate clusters of the minute ani- 

 mals, (fig. 253,) which are imbedded in it ; each of these has a small 

 circular orifice toward the outer end, opening into the gill cavity, and 

 another orifice opening into a larger cavity in the center of the cluster, 

 which is common to all those in the cluster ; and it has a central exter- 

 nal orifice, through which the waste water from the gills, the faeces, 

 and the eggs are discharged. These young colonies begin to appear in 

 June and grow very rapidly, new individuals being formed by buds that 

 originate from the first ones in rapid succession, so that in two or three 

 weeks the small colonies will increase from a quarter of an inch in 

 breadth up to three or four inches, if they be situated on a flat sur- 

 face and have room to spread. If upon the stem or leaf of the eel- 

 grass they will extend entirely around it, and perhaps several inches 

 along its length, if not opposed by other colonies. At the same time the 

 crusts increase very much in thickness. Thus by the end of the summer, 

 the eel-grass, algie, stems of hydroids, &c., often become completely 

 covered up b}' the luxuriant growth of this curious compound animal. 

 The colors of this species are extremely variable and often very elegant, 

 and it is seldom that two colonies can be found with precisely the same 

 pattern of color. Growing ui)on the same leaf of eel-grass, many dif- 

 ferent colonies may often be found, each showing a difterent arrange- 

 ment of the colors. 



In one of the most common varieties the general color of the common 

 tissue between the stellate clusters is dull olive-green, thickly specked 

 with small flake-white spots, which are formed by the enlarged terminal 

 portion of stolon-like processes, which bud out from the perfect individu- 

 als composing the clusters, and are arranged somewhat in circles around 

 the clusters ; the lower portion of these stolons is usually yellow or 

 orange, and the outer part deep purple, tipped with flake-white. The 

 individual animals, or zoiiids, composing the stellate clusters, are deep 

 purple, with the branchial orifice yellowish white, surrounded by a circle 

 of orange ; a short flake-white longitudinal line runs along the middle of 

 the upper side, interrupted by the branchial opening, but this line is 

 often represented only by two white spots ; other flake-white spots are 

 usually irregularly scattered over the outer end. 



