ZOOPHYTES. 1 9 



organ is indicative of a comparatively low grade of organiza- 

 tion, and is found only in the lower divisions of the radiate 

 group. An example of this occurs in the numerous stomachs 

 of the Polygastrica, and in the ova-producing segments of the 

 body of one of the Entozoa. The multitude of hungry mouths, 

 each collecting food for the entire group, may he regarded as 

 another instance of the same kind of structure. All the cells 

 are not alike. Among them are some of a larger size and 

 different form, which, from their containing the germs or ova, 

 are termed " ovigerous vesicles." 



The ova found in these vesicles are covered with hair-like 

 cilia, which have the power of vibrating continually. By 

 means of these, they are able to diffuse themselves over the 

 bottom of the sea, and to swim about for a day or two, until 

 they find a fitting place for their future habitation, and for 

 the establishment of new and populous colonies. When the 

 animal becomes fixed, it first spreads a little, so as to form a 

 secure base; next, cells are observed; then branches teeming 

 with their busy occupants are developed, and the coralline 

 assumes the form characteristic of the species. 



Some calculations have been made respecting the number 

 of individual polypes contained in some of these structures. 

 A single plume of a species found upon our shores has been 

 estimated to contain 500. " A specimen of no unusual size 

 has twelve plumes; thus giving 6,000 polypes as the tenantry 

 of a single polypidom! Now, many such specimens, all united 

 too by a common fibre, and all the offshoots of one common 

 parent, are often located on one sea-weed; the site, then, of 

 a population which nor London nor Pekin can rival! "* With 

 regard to the growth of these corallines, it has been observed 

 that the lower cells are developed soonest, and, after a season, 

 drop off altogether. But " there are facts which appear to 

 prove that the life of the individual polypes is even more 

 transitory; that like a blossom they bud and blow, and fall off, 

 or are absorbed, when another sprouts up from the medullary 

 pulp to occupy the very cell of its predecessor, and, in its 

 turn, to give way and be replaced by another, "j 



Many of these animals possess luminous properties. If 

 some of them, on the frond or broad-spreading leaf of a sea- 

 weed, are subjected to a sudden shock, they give out an 



* Plumularia cristata. Johnston's Zoophytes, p. 144. 

 t Idem, p. 89. 

 VOL. i. B 2 



