INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 327 



and thrown overboard, as is sometimes done, each ray has the power of 

 reproducing all the lost parts, so that each fragment may, after a time, 

 become a perfect star-fish. 



The color of this species is generally dark green or brownish green, 

 with the madreporic plate bright orange ; the males are more inclined 

 to browD, and sometimes have a reddish tint. It is found all along the 

 coast from Massachusetts Bay to Florida. 



The eggs of this species, like those of most other star-fishes, produce 

 peculiar larvae, entirely unlike the parents, and provided with vibrating 

 cilia by means of which they swim about in the water, or at the surface, 

 for a considerable time. The young star-fish develops within the larva 

 and gradually absorbs the substance of the larva into its own organi- 

 zation. 



The development of this and our other common species has been very 

 fully described and illustrated by Mr. A. Agassiz. 



Of the Hydroids many species occur in the pools, or attached to th e 

 lower sides of overhanging rocks, or of stones that have an open space 

 beneath them, or growing upon the Fucus and other sea- weeds at low- 

 water mark. The most abundant of all is the Sertularia pumila, (Plate 

 XXXVII, fig. 279,) which grows in small tufts of delicate branches on 

 the stems and fronds of all the larger sea-weeds, and on the sides and 

 lower surfaces of stones. Another beautiful species, the Obelia commis- 

 siiralis, (Plate XXXVII, fig. 281,) occurs at low- water mark and in tide- 

 pools, attached to stones and sea-weeds. It is very delicate and much 

 branched, and sometimes grows five or sis inches high, though usually 

 smaller. At certain times it produces small niedusse in its urn-shaped 

 reproductive capsules ; these are discharged and swim free for sometime, 

 having sixteen tentacles when they become free. Several other spe- 

 cies of this genus also occur attached to the sea-weeds at low-water. 

 The most common of these is 0. diaphana, which grows about an inch high, 

 attached to the stems of Fucus. The Campanularia flexuosa is another 

 similar hydroid, remarkable for its large reproductive capsules, in which 

 medusae are developed that never become free. This species occurs 

 in the pools at low-water, on weeds and stones, and also on the lower 

 sides of overhanging rocks or the timbers of wharves. It is much 

 more abundant farther north, as at Eastport, Maine, where it grows in 

 profusion on the timbers of the wharves, hanging down from their 

 lower sides, collapsed and dripping, while the tide is low. The Pennaria 

 tiarella (Plate XXXVII, figs. 277, 278) is a very conspicuous and beau- 

 tiful species on account of its much -divided black branches and numer- 

 ous bright red flower-like hydroids. It occurs occasionally in the pools, 

 and just below low-water mark, attached to stones, corallines, &c, but is 

 more common in somewhat deeper water on rocky and shelly bottoms. 

 The "file-fish" feeds on this species, and probably on other allied 

 hydroids, for its stomach was found full of the stems and branches, 

 cut up in fine pieces. Its broad, sharp-edged 'jaws are admirably 



