144 Dr. G. C. Wallich on the Value of 



where the capillary channel has been somewhat extended and 

 sealed up at one end under the action of the blowpipe. 



In a former communication {' Annals/ May, p. 367) at- 

 tention was drawn by me to the occasional occurrence of a 

 funnel-shaped tubule which opened out in the midst of the 

 villous organ; and it was stated that when this took place, 

 no contractile vesicle was observable. It was also stated that I 

 had seen effete particles, and, on three occasions, bodies which 

 resembled vacuoles, extruded through similar orifices. More 

 recent observations, however, have satisfied me that the failure 

 to detect the contractile vesicle during periods which I then 

 considered sufficient to ensure the occurrence of the diastole or 

 systole may have been due to the insufficiency of those periods, 

 and hence that this organ may have been present notwithstanding 

 its having escaped notice. The guarded manner in which I 

 stated what took place was the result of a doubt as to whether 

 the tubule was formed by the contractile vesicle, or by a vacuole, 

 or was in reality an extemporized channel. The opinion I now 

 hold — one based on actual observation — is, that whereas in some 

 cases a food-vacuole may be reabsorbed into the substance of 

 the body after the effete matter it contained has escaped, and in 

 this way be converted into an infundibuliform tubule, in others 

 the vacuole may be discharged along with the effete matter 

 which it encloses, and the tubule may be produced in the sub- 

 stance of the body at the point of extrusion, — the first of these 

 appearances presenting itself when the effete mass is of a shape 

 admitting of easy discharge as soon as the margin is reached, 

 the second when the mass is so irregular in outline as to en- 

 tangle its own vacuole and carry it along with it. 



According to my experience of A. villosa, it seems almost 

 certain that, normally, the contractile vesicle is single, and that 

 the evolution of supplementary vesicles from the primary one, 

 in the manner already described, may take place without refer- 

 ence to approaching fission. For, did the evolution invariably 

 precede that process, we should, in all probability, detect a 

 plurality of nuclei also, which is not always the case. And, 

 unless we regard fission in these lower organisms as an accidental 

 phenomenon, the supplementary vesicles, when once detached 

 in such cases, would not coalesce again with the primary one. 

 On the other hand, there is every reason to believe that, when 

 fission takes place normally, each segment is provided with its 

 own nucleus and contractile vesicle. I say normally, because 

 examples havq been observed by me, from the commencement to 

 the end of the process, in which sometimes the nucleus, and 

 sometimes the contractile vesicle was absent in one of the newly 

 formed segments. But I must mention that, whenever the 



