﻿Sponges. 



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fcion of a stomach or internal cavity in the body of the ciliated larva. 

 After swimming about for a time it becomes fixed by the end of the body 

 to some object, the cavity finally opening out by a mouth. Afterward 

 the true sponge character of the organism is revealed. The body wall 

 becomes perforated with pores, which open into the general cavity of the 

 body, while currents of water are maintained by means of the cilia, and 

 flow out through the so-called mouth. This is the proto-spongia state, and 

 when spicules of silex or lime are developed to strengthen the walls of the 

 body, the young sponge is termed the "Olynthus." 



Hartwig says of the Porifera, or sponges, that they were formerly sup- 

 posed to belong to the Vegetable Kingdom, but their animal nature is now 

 fully ascertained. For modern research has proved that the soft glairy 

 substance with which their skeleton is invested during life, consists of 

 "sarcode" similar to that which forms the soft parts of the Foraminifera 

 and Polycystina. It is by this animated or organic gelatine, which can 

 generally be pressed out with the finger, and in some species is copious to 

 nauseousness, that the solid parts of the sponge are deposited, and from it 

 the whole growth of the mass proceeds. 



The framework or skeleton of the Porifera is usually composed of* horny 

 fibers of unequal thickness, which ramify and interlace in every possible 

 direction, anastomosing with each other, so as to form innumerable contin- 

 ous cells and intricate canals, the walls of which in the recent sponge are 

 crusted over with the gelatinous living cortex. Generally this fibrous 

 mass is interwoven with numerous mineral spicules of a wonderful ele- 

 gance and variety of forms, for their shapes are not only strictly deter- 

 minate for each species of sponge, but each part of the sponge, it is 

 believed, has spiculae of a character peculiar to itself. Sometimes they 

 sire pointed at both ends, sometimes at one only, or one or both ends may 

 be furnished with a head like that of a pin, or may carry three or more 

 diverging points, which sometimes curve back so as to form hooks ; some- 

 times they are tri-radiate, sometimes stellar; in some cases smooth; in 

 others beset with smaller spinous projections like the lance of the Saw 

 Fish. In many species they are imbedded in the horny framework ; in 

 others, as for instance, in Tethia Cranium, or in Halichondria, they project 

 from its surface like a tiny forest of spears. They are generally composed 

 of silex or flint, but in the Grenus Grantia they consist of carbonate of 

 lime. 



Though the skeleton of most sponges is formed both of horny fibers and 

 of mineral spicules, yet the proportions of these two component parts vary 

 considerably in different species. In the common sponge, for instance, the 



