124 



TOILERS IN THE SEA. 



The essential feature of the flagellate monads is, 

 that they possess a film-like collar of membrane, not 

 unlike a little funnel, which is capable of extension 

 or withdrawal, enclosing within it a terminal flagellum, 

 or whip-like thread, and at the other extremity con- 

 tractile vesicles (fig. 18). As to the collar, it is 

 stated to be not a mere funnel-shaped expansion of 

 inert sarcode, but a most active organ, having, dur- 

 ing life and when fully ex- 

 tended, a continuous stream 

 of fine granular protoplasm 

 for ever flowing up the ex- 

 terior, and down the interior, 

 surface of the collar, identical 

 with the cyclosis exhibited 

 in the pseudopodia of Fora- 

 minifera. It has also been 

 demonstrated that " this 

 collar, with its characteristic 



currents, is an exquisitely contrived trap, for the 

 arrest and capture of its customary food, which, 

 driven by the action of the central flagellum against 

 the outer margin of the collar, adheres to it, and 

 passes, with the onflowing protoplasmic stream, into 

 the animal's body." These collared monads are 

 always found lining special cavities, excavated within 

 the hyaline mucous-like stratum (or cytoblastemd). 

 There is, of course, in different sponges, variability in 



FIG. l8. COLLARED 



MONADS (Halichondria pa- 

 nice a). 



