Treshwater Biyozoa, with descriptions of new Species. 203 



tella Allmani : a, mouth ; b, oral valve ; c c, oral arms ; d, mem- 

 brane at base of tentacles. 

 Fiff. 4. Much-enlarged view of the reproductive organs of Fredericella sul- 

 tana : a a, outer wall of cell ; b b, lining membrane or tunic ; 



c, lower portion of stomach ; d d, ovary ; e, egg imbedded in same ; 



f, two filaments attached to the lower end of stomach, probably 

 connected with the reproductive system ; g, retractor muscles. 



Fig. 5. Enlarged view of a cell of Plumatella Allmani exhibiting reproduc- 

 tive organs : a, base of oral arms ; b, oesophagus ; c, stomach ; 



d, intestine ; e e', ovary ; /, egg nearly mature, still attached to 

 ditto ; g, an egg just forming likewise attached to ovary ; h h, two 

 filaments attached to the stomach, probably connected with the 

 reproductive system ; i i, the two bundles of retractor muscles ; 

 j, outer wall of cell ; k, lining membrane or tunic. 



Plate IV. 



Fig. 1. Enlarged view of a cell of Paludicella procumbens seen as a trans- 

 parent object, the polype being exserted : a a, outer wall of cell ; 

 bbb, lining membrane or tunic ; e, tubular orifice ; d, membranous 

 cup surmounting ditto ; e, tentacular disc ; /, tentacles ; g, pha- 

 ryngeal swelling ; h, cesophagus ; i, stomach ; j, intestine ; k, en- 

 largement at commencement of ditto ; I, anus ; m, supposed ovary ; 

 n, filament attached to the lower extremity of stomach, probably 

 connected with the reproductive system ; o, polype retractor 

 muscles ; pp, inferior tube-retractors ; q, two fibres of superior 

 tube-retractors ; r r, muscles to prevent the complete inversion of 

 tentacular sheath ; s, tentacular sheath doubled upon itself ; t, pa- 

 rietal muscles; u, end- walls of two cells abutting against each 

 other. 



FH,g. 2. Enlarged view of a single cell of P. procumbens with polype re- 

 tracted : a, outer wall of cell ; b, lining membrane of ditto ; c, re- 

 tracted tubular orifice ; d, tentacles ; d' d', tentacular sheath ; e, 

 oesophagus ; /, carcUac orifice ; g, stomach ; h, intestine ; i, enlarged 

 portion of ditto ; j, supposed ovary doubled upon itself; k, filament 

 attached to lower end of stomach, probably connected with repro- 

 ductive system ; 1 1, polype retractor muscles ; m m, inferior tube- 

 retractors ; nn, superior tube-retractors ; o, sphincter muscles for 

 closing orifice ; p, do. do. ; q q, muscles to prevent complete in- 

 version of tentacular sheath ; r, end-wall of cell formed by the 

 tunic exhibiting enlargement in the centre. 



F^g. 3. End of retracted tube of P. procumbens exhibiting the manner in 

 which it folds in. 



Fig. 4. Termination of a branch of P. procumbens comprising two cells in 

 difi^erent stages of development : a, outer wall of cell in fourth 

 stage of development ; b, lining membrane of ditto ; b', blind ter- 

 mination of do. do. ; c, place of future orifice ; d, tentacles of 

 polype in state of development ; e, oesophagus ; f, stomach ; g, in- 

 testine ; h, lower reproductive organ ; i, tentacular sheath ; j, po- 

 lype retractor muscles ; k, tube-retractors ; /, new cell in first or 

 earliest stage of development, exhibiting hning membrane and ex- 

 ternal wall ; m, nucleated cells in lining membrane. 



FH,g. 5. Two terminal cells of P. procumbens containing buds in different 

 stages of development : a, tentacles of bud far advanced or in 

 fifth stage of development ; a', tentacular sheath ; b, cesophagus ; 

 c, stomach ; d, intestine ; e, anus ; /, lower reproductive organ ; 



g, polype-retractors ; h, parietal muscles ; i, tube-retractors : j, tube 



