194 Prof. H. James-Clark on the Spongias ciliatas 



gradually reverses the arc and, assuming a much stronger bend 

 in the opposite direction, terminates abruptly, and far beyond 

 the edge [h^) of the collar, with about the same thickness as at 

 its base. It is a very conspicuous organ, and therefore its whole 

 sigmoid length may be studied with any amount of detail that 

 could be wished for. The plane of this sigmoid curve is a 

 direct continuation of that which passes through the opposing 

 longer and shorter curves of the obliquely oval body. Calling 

 to mind now what has been said in regard to the direction of 

 the curve of the flagellum of the respective individuals of the 

 colony, it will be seen that if these planes are projected in- 

 wardly and downwardly, at the same time passing along the 

 pedicels (fig. S,2yd'^) of each body, they will all meet at the 

 main stem (pc?). 



Besides being used as an organ of prehension, the flagellum 

 is occasionally devoted to other purposes, — for instance, to act 

 as a scavenger by whirling in a gyi-atory manner, and thus 

 clearing the area within the collar of fascal matters which have 

 been ejected from the anus at a point near to, or perhaps co- 

 incident with, the mouth {in). At other times it acts as an 

 organ of propulsion during the act of natation (fig. 23), when 

 one of the resultants of self-division breaks loose from the 

 colony and seeks another point to settle down upon and secrete 

 its stem. During this wandering life of the Monad it swims, 

 at times very rapidly, with its basal end (fig. 23) preceding it 

 in the direction of its course, and the flagellum (fl) following 

 behind and vibrating in rapid undulatory and gyratory curves, 

 as if it were the screw propeller of some subaqueous vessel. 



That the mouth (figs. 23, 24, 24^, m) is situated near the 

 base of the flagellum {fl.) is rendered certain by the fact that 

 particles of food are thrown by that organ directly against the 

 area (//■) upon which it is based, and are taken within the 

 body somewhere in that region ; but, on account of the minute 

 size of these morsels, and the rapidity with which they are 

 swallowed, it has not been possible to determine precisely at 

 what point. The position of the anuSy which, as I have al- 

 ready suggested, may possibly be coincident with the mouth, 

 is easily determined, even to the narrowest limits, as the fjEcal 

 matter is discharged in large, highly refractile pellets (fig.24^,c?) 

 close to the base of the flagellum. The digestive vacuoles are 

 quite conspicuous, and frequently very large ; but they never 

 have been observed to be so numerous as to obscm-e the view 

 of the interior of the body. 



The contractile vesicles (cy, cv) are two quite conspicuous 

 globular organs, which lie close to the surface and in the pos- 

 terior third of opposite sides of the body. Occasionally thi-ee 



