ZOOLOGY. 343 



the texture is usually porous. But nature is not without an expedient 

 to prevent a catastrophe that would be destructive to a large part of 

 growing zoophytes, and would prevent the indefinite increase just 

 explained. The dead surface becomes the resting-place of numberless 

 small incrusting ^species of corals, besides Nullipores, Serpulas, and 

 some mollusks. In many instances the lichen-like Nullipore grows at 

 the same rate with the rate of death in the zoophyte, and keeps itself 

 up to the very limit of the living part. The dead trunk of the forest 

 becomes covered with lichens and fungi, or, in tropical climes, with 

 other foliage and various foreign flowers : so, among the coral pro- 

 ductions of the sea, there are forms of life which replace the dying 

 polyp. The process of wear is thus entirely prevented. 



The older polyps, before death, often increase their coral secretions 

 within, filling the pores occupied by the tissues, and rendering the 

 corallum more solid ; and this is another means by which the trees of 

 coral growth, though of slender form, are increased in strength and 

 endurance. 



The facility with which polyps repair a wound, aids in carrying for- 

 ward the results above described. The breaking of a branch is no 

 serious injury to a zoophyte. There is often some degree of sensibility 

 apparent throughout a clump, even when of considerable size, and the 

 shock, therefore, may occasion the polyps to close. But in an hour, 

 or perhaps much less time, their tentacles will have again expanded ; 

 and such as were torn by the fracture will be in the process of com- 

 plete restoration to their former size and powers. The fragment 

 broken off, dropping in a favorable place, would become the germ of 

 another coral plant, its base cementing by means of coral secretions to 

 the rock on which it might rest ; or, if still in contact with any part 

 of the parent tree, it would be reunited and continue to grow as before. 

 The coral zoophyte may be levelled by transported masses swept over 

 by the waves ; yet, like the trodden sod, it sprouts again, and continues 

 to grow and nourish as before. The sod, however, has roots which are 

 still unhurt ; while the zoophyte, which may be dead at base, has 

 a root a source or centre of life in every polyp that blossoms over 

 its surface. Each animal might live and grow if separated from the 

 rest, and would ultimately produce a mature zoophyte. /. D. Dana, 

 Geology of the U. S. Exploring Expedition. 



ON TIIE IIOLOTIIURIDJS OF THE NEW ENGLAND COAST. 



MR. AYRES, of the Boston Xatural History Society, who has recently 

 been engaged in the careful study of the Holothuridae of the New 

 England coast, has given the following as the result of his investiga- 

 tions, as communicated to the society : 



Thirteen species have been described, included in eight genera. Of 

 these, three genera and eight species are believed to be new. The fol- 

 lowing list gives, with the name of each species, the depths through 

 which it has thus far been observed to range : Synapta tennis, Ayres, 

 littoral to six fathoms; Chirodota arenata, Gould shoal water: 

 Sckrodactyla briareus, Le Sueur littoral to four fathoms ; Thyoni* 



