OF MICR O- OR GANISMS. 99 



fragment without nucleus contains the mouth; the 

 mouth ingests alimentary substances. If the Cyrtosto- 

 mum be given grains of potato fecula, which it is very 

 partial to, the fragment without nucleus, but with a 

 mouth, swallows these grains and fills itself with them. 

 It is not known whether it digests them. 



This much was observed in the first stages, and 

 Gruber was wrong in stopping at this point. 



At the expiration of a certain time, varying be- 

 tween the third and fourth day, alterations of structure 

 are noticed in the fragment that are probably traceable 

 to the absence of the nucleus. One of the first to take 

 place is the disappearance of the marks of differentia- 

 tion which we have observed to distinguish the endo- 

 plasm from the ectoplasm. The dark granules that 

 fill the interior of the body congregate in the centre 

 by abandoning the peripheral part; then these granules 

 scatter and come to a position just beneath the cuticle, 

 which denotes a deliquescence of the plasma. The 

 layer of trichocysts undergoes changes and disap- 

 pears. All these alterations result from an actual dis- 

 organization of the plasma. The contractile vesicle 

 shrinks, its pulsations decrease, the radiating passages 

 disappear. The body of the animal, which in its nor- 

 mal condition is elongate, becomes rounded; its move- 

 ments flag and consist of nothing but a rotation of 

 the body about its own axis; at last the animal be- 

 comes motionless and dies of diffluence. 



These changes are not due to lack of sustenance, 

 as one might suppose; for fragments that have a 

 mouth and swallow food, pass through the same alter- 

 ations as those that have no mouth.* 



* M. Balbiani has informed us, upon request, that the fragments of Cyr- 

 tostomum furnished with nucleus can be kept alive for a much longer time 



