(AS 



I'UOTUZU A. 



THE ASTASID^. 



Tlu'so aro disliiiixiiisliod by an extremely coiitructilo body, generally of a greener red color. 

 TIk' KiK/hiKt rlridin (sec page 040) is very contractile and assumes various forms ; it often ap- 

 pears 111 Uie water iii sueli myriads as to make it appear of a green color. 



THE I'ElUDINIDiE. 



In this faiiiilv the species are provided with a silicious case or carapace, furnished with an 

 opening which has a circlet of cilia: the shell is often produced into curious horn-like processes. 

 Nlotion in these animals is not only ctfccted by the cilia, but also by the aid of filiform appeiid- 

 jigcs protruded from the carapace. 



THE OPALINIDJi;. 



These animals arc colorless, of a glassy transparency, moving by cilia arranged in oblique lines, 

 upon their flat, oval bodies; they have only been found as parasites in the intestines of frogs and 

 certain worms. 



Class 11. PORIFERA. 



This term is from the Latin porus, pore, and fero, to bear, and the animals to which it refers 



are popularly called Sponges. These 

 are generally regarded, and perhaps 

 justly, as standing on a sort of debat- 

 able ground between the animal and 

 vegetable kingdoms, or at all events as 

 occupying a frontier station in the 

 former and approaching more closely 

 to plants than any other animated be- 

 ings. Sponge, in the state in which 

 we usually see it, consists of a congeries 

 of horny filaments, interlaced in every 

 direction so as to form an intricate 

 net-work of intercommunicating cells. 

 Imbedded in these threads, in the ma- 

 jority of sponges, are a number of very 

 minute needle-pointed siliceous or cal- 

 careous particles of various forms ; 

 these are called sjncula. In most cases, 

 the spicula are simply of an acicular 

 form, slender and cylindrical, and 

 pointed at both ends. In other instances they have a small knob at one end, while the 

 opposite extremity is pointed, giving them exactly the appearance of minute pins ; in others, 

 again, we find one end transformed into a fork with two or even three prongs; or the whole 

 spiculum consists of three or four spines of equal length. This framework, with its contained 

 spicula, is, however, only a sort of skeleton, on which the true living portion of the sponge is 

 supported. This consists of a coating of gelatinous matter, which is spread over all the fibers of 

 the reticulated skeleton ; its consistence is very like the white of an egg, and it runs freely away 

 from the sponge when the latter is taken out of the water. But when examined under the 

 microscope, this gelatinous coating is found to consist entirely of an immense number of aggre- 

 gated sarcode-cells, exactly resembling the Am<xba, the simplest type of the Rhizopoda, which 

 we shall hereafter describe. Like that curious creature, each of these cells appears to possess 

 a perfectly independent existence ; each presents one or more contractile spaces ; and even 



SPONGES OF VAlilOLIS FORMS 



