16 Prof. H. James-Clark on the Animality of the Ciliate Sponges, 



almost incessant spasmodic incurvation toward the mouth, to all 

 appearance for the purpose of throwing or jerking particles 

 of food in that direction. When an acceptable morsel is met 

 with, both the lip and the flagellum combine to press it into 

 the open jaws of the animal ; and when that is accomplished, 

 the two organs immediately return to their former positions. 



Scarcely less noticeable is the so-called contractile vesicle — the 

 analogue of the heart of the higher animals. In a view of the 

 body so placed that the lip is next the eye, and the flagellum 

 consequently curving away from the observer, we have the two 

 broad sides on the right and left, and the plane of the greater 

 transverse diameter coincident with the line of vision. The body 

 then seems, at first sight, to have a symmetrical aspect, such as 

 is not observable from any other point of view; and such it 

 might be made to appear if I should belittle the importance of 

 one single organ, by simply mentioning its existence and omit- 

 ting k) lay down its exact topographical relationship. I refer to 

 the contractile vesicle. During the systole of this organ it is so 

 inconspicuous that it would easily escape even the most careful 

 observation ; but during the transition to the expanded state, 

 and at the full diastole, its prominence, from the point of view 

 just mentioned, is so great as to rival the flagellum in attraction. 

 It may then be seen as a comparatively large, rounded, trans- 

 parent, vesicular body, which stands out in strong profile, just 

 in front of the middle, and close to the surface of the left side of 

 the body. At full diastole it even forces the overlying region 

 outwardly into a quite prominent papilla. In reference to the 

 other organs and parts of the body, it stands, therefore, alto- 

 gether in an asymmetrical relation ; and from whatever point of 

 view it, or any of the organs, may be observed, the organiza- 

 tion as a whole evidently rests upon an oblique basis. The bi- 

 laterality of the type is sufficiently clear ; but the topographical 

 relationship of the organs is incompatible with bisymmetry, for 

 right and left are twisted upon each other. 



So much for Monas. As for the objection which has been 

 raised against the estimate that has been put upon the monad- 

 like Infusoria, because they have not been proved to be adult 

 forms, it seems to me that the onus of proof lies on the other 

 side, viz. to show that they are not adult. I think, moreover, 

 that I am fully warranted in assuming that a Monas which pos- 

 sesses such an organization as I have described, and is attached 

 to a stem, is an adult ; and more especially so since, among many 

 hundreds which I have observed from time to time, I have never 

 seen any trace of a transition to a higher form. That such 

 simple organizations can exist without rising to a more compli- 



