64 DAVENPORT ACADEMY OF SCIENCES. 



Nucleus band-like, curved, centrally located. Contractile vesicle 

 posterior. 



I,ength, 100-175 microns. 



Figure 96, Plate XIII, represents a typical individual of this 

 species. In its motion Didiiiiiivi nasutuin is swift, rolling on its 

 longitudinal axis, darting from side to side, then suddenly stop- 

 ping in its flight, with the anterior end downward, it whirls rap- 

 idly for a few seconds, then continues its random course. 



The food habits of Didiniuvi nasiUmn present some interesting 

 features, the organism being found associated with Paramcechun, 

 which serves as its principal food. It is fierce and aggressive, 

 grasping its prey with the snout-like proboscis and literally gulp- 

 ing it down whole, the process requiring but a few seconds. 



Balbiani, the French naturalist, records that the proboscis may 

 be protruded even to the length of the body and by this means 

 Didiniiim grasps its prey and sucks the contents or transfers it 

 whole to its own body by the retraction of the proboscis. My 

 observations have not verified this; in fact, at no time in the 

 scores and scores of instances in which Paramisciwn has been 

 observed to become the prey of Didinhim, was there a protrusion 

 of the snout-like process, but the animal approached and, striking 

 its prey with the unextended proboscis, proceeded to swallow it 

 whole. The striking results in a paralyzing effect upon Paramce- 

 chim, its struggles ceasing almost immediately. 



Sometimes Paramcccium is grasped near the middle instead of 

 at the end, in which case Didiiiium, instead of entirely releasing 

 its prey, by a quick, jerky movement shuffles along until one 

 extremity of the "slipper-animalcule" is reached, then the inges- 

 tion takes place. 



Figure 97, Plate XIII, is drawn from a mounted specimen fixed 

 during the process of ingestion of ParanucciKni. 



Reproduction takes place by transverse fission, preliminary 

 steps to constriction of the body being the elongation of the 

 nucleus and the appearance of two supplementary wreaths of cilia. 



A very definite flow of protoplasm within the body may be 

 observed, the endoplasm flowing toward the anterior extremity 

 along the periphery, then turning inward and uniting in a com- 

 mon backward stream along the longitudinal axis, separating in 

 the posterior region, turning outward and flowing forward again. 



