The Life History of Tillina Magna 41 1 



VII REGENERATION AND CENTRIFUGING 



The experiments of Nussbaum ('88) on Oxytricha and Gastro- 

 styla, of Gruber on Stentor, of Balbiani ('88) on Trachelius and 

 Prorodon, of Verworn ('95) on Thallassicolla, all prove that non- 

 nucleated fragments of protozoa will not develop while nucleated 

 fragments regenerate easily. A few experiments were performed 

 with Tillina. A single individual was placed in as small a drop 

 of water as possible. Then by the aid of a simple microscope, 

 transverse, longitudinal or oblique cuts were made with a sharp 

 scalpel. The individuals being minute and constantly moving, 

 made the operation somewhat difficult, and often but one-half 

 would live, the other being crushed by the knife. Eight success- 

 ful experiments were performed in which a longitudinal cut was 

 made. Of these, six left halves regenerated in 24 hours, and two 

 right halves. Ten transverse cuts were made, and in two cases 

 both halves regenerated. Of the other eight, four posterior and 

 four anterior halves regenerated, showing that there is no differ- 

 ence in the regenerative power of the anterior and posterior regions. 

 In two cases regeneration, growth to normal size, and a single 

 division took place within 24 hours. Only a few oblique cuts 

 were made, and these were unsatisfactory, as one section was too 

 small to regenerate. On the whole, Tillina has a remarkably high 

 degree of regenerative power. Regeneration, however, will not 

 take place if the halves are put into tap water. They seem to 

 require the full degree of density in order to recover their normal 

 conditions. 



Experiments were made centrifuging four groups of ten indi- 

 viduals each 50, 100, 300, and 500 times respectively. The 

 results were not definite, lack of material preventing extensive 

 experiments. In all the centrifuged individuals, the nucleus 

 tended to be shifted forward. In those centrifuged 100 times 

 practically all of the nuclei were sent to the anterior end of the 

 body. Those centrifuged 300 times showed a scattering of the 

 pigment throughout the body, as well as a shifting of the nucleus. 

 In one case among those centrifuged 500 times, the pigment was 

 sent in a mass to the anterior end, together with the nucleus. In 



