120 ^t\ MO^j'e i>r Fitrijiifnt. 



the xvater enters at the pore*, ixh,**^"* thtv^u^h the vario-.i-i canals and 

 eaTitie*. and tinally leave* the Sivr.irx^ by the . <v">.:a. Mi.-A><v\»pic 

 particles, which serve lor the nonrishment of the animal, enter with 

 the water; the coUar oeHs take these np, and later, ejec: the 

 uiiviiiT^sr^v, portior.s. The current of water is nndoubtedly also i>f 

 the arreatest importance f*>r :vspiri»tion. 



In some sjv^rce-s tl»» pores le«d mtv'» •>r^l>i:\llsr cavities vvowning below 

 the s-.vr;a^v. the snbeortieal orypts. t;v:^- wltieh oanals ariae suni 

 mn to the flagellate ehauitiers. 



rhe middle layer notiivd above forms the chief '. .;i^s of the Ixxly, 

 it tisnally CvMisisrs et a Svn-i of connective :issr.e with ir*:^latii'-er,s inter- 

 cellular snbstance. In this tissue, 1h siues lixed cel.s - >me of which 

 may be piiTKientevi' , there are a m o? b o i d w a n d e r i n ar cells 

 which move about in the mas* i>t jelly. Here :.lso hard j>arts are 

 almost always developed and form a m«.iire or '.ess wnnected 

 skeletoij, n-.is ee^asisrs either of a netwv^rk of horny tibres; 

 or of fine c a 1 o a r e o n s spicule s, which may be s;>.v.y!e, or 

 possessed of three or four brandies, radiating out in vsitYe-.vni 

 directions ; or theiv is a s i 1 i c i o'« s skeleton v^f a very diflfetvnt 

 kind, composed of isv^lated spicules cv>nnected by a wa^s of ivinent 

 substv^iKV. oa- of silicious tibres. The >i:icious spicules aiv 

 either simple and needle-like, or of more oov.'.viie.ueil and often very 

 beautiful forms ^aiiohoi-s, asiers, etc,^. Not infrequently the 

 calcaivous or silieions spi>"ules project partially from the surface 

 of the Ixxly. In some Spoiit^^s the skeleton is exehisive.y 

 calcareous ; in others entirely silicious ; in others apiin, horny. 

 In many forms, however, it is both horny and silicious, ihouirh 

 ealeaivous spicules and horwy tibres never >.veur lOiTt^ther. Besides 

 the struoTuivs already mentioned muscle eells aiv pivsent in the 

 middle layer; and it is sjiiil that nerve cells aiv al>o found 

 there. In some S}x>iiires suportieial sensory cells are pivsent 

 in certain ivgions. 



Very frequently Spongi^s multiply asexnallv, forming- colouie* 

 of vario\is kinds, the individtials of which are only in a few 

 cases clearly ilistins^nishable, whilst they are, for the most pirt, 

 so intimately connected with their neighbours that, externally, the 

 number of osenla alone pwnes that there is moiv than one individual. 

 In some forms, however, after ijennnation, the new individuals 

 separate ofif and develop indepeiuiently. In Vrt>sh-water Spoiiijvs 

 there is a peculiar mode of asexual it^pivdnetion : portions of the 

 animal encvst in small eaps>iles formed within it, and after a 

 ivsting- staare develop into new individuals ^yitmmu}{f\. 



"With these t xoeptions, Spougvs ivpt\»dnee in the usual way by 

 ova and spermatozoa, which aiv formed either in the sjune 

 individual or colony, or in different ones. The ovum is naked and 

 capable of anu^boid movement ; it develops within the Ivnly of the 



