METAZOA PORIFERA. 81 



to the peculiar spicules just named there are two other 

 kinds of spicules forming the skeleton and strengthening 

 the dermis. An interesting specimen allied to Spongilla 

 lacustris has been described by Edward Potts. This 

 sponge is found incrusting marine organisms such as bar- 

 nacles and the calcareous tubes of Serpula, in the fresh 

 water of a creek in the southwestern part of Florida. 

 The presence of the barnacles can only be accounted for 

 by the action of the strong southeast winds which back 

 up the salt water into the rivers and creeks. The young 

 barnacles, having followed the influx of salt water and 

 attached themselves to the rocks on the bottom, may have 

 attained a portion of their growth while immersed in fresh 

 water after the subsidence of the salt water. If this be 

 true it is suggestive of the possibility of the conversion of 

 the marine barnacle into a fresh-water species. The 

 sponges already spoken of as occurring on these animals 

 have the peculiar habit of hiding away the winter buds 

 within the barnacles or in the tubes of the Serpula. 



A sponge (Reniera), closely related to the Chalinula 

 next to be described, is said to possess thread cells or 

 nematocysts which were formerly supposed to be the 

 exclusive possession of the next branch, the Coelentera, 

 but which have already been found in the Protozoa. In 

 this group the embryo has a pigmented spot on one end 

 of its oval body which may perhaps be considered as an 

 eye. 1 



Chalinula oculata Pallas is of especial interest to New 

 Englanders since it grows abundantly along the eastern 

 coast. In this sponge the spicules are straight and exist 

 as vestiges, while the horny matter has increased in 

 quantity. 



Keller 2 has observed and figured the consecutive stages 



1 Lendenf eld, Mon. Australian Sponges, Proc. Linn. Soc. New 

 South Wales, IX, part 2, 1884, p. 324. 

 2 Zeitschr. f. wiss. Zool., XXXIII, 1880, p. 317. 



