268 C. M. Child. 



gradually disappear. The branches do not simply become 

 invisible or difficult to see because of loss of contents but the distal 

 portions actually disintegrate. The disintegration occurs not only 

 in the new parts but in the old as well, though not indicated in the 

 figures, so that in these stages only the more central parts of the 

 intestine remain. Some consideration of these changes has been 

 given in previous papers (Child, '04b, '04c) but other species are 

 more favorable for experiment along this line. These cases sup- 

 port the suggest ons reached in the other papers on Leptoplana 

 regarding the effect of internal mtestinal pressure on form and 

 extent of the intestinal branches. 



B. THE EXPERIMENTAL PRODUCTION OF ABNORMAL FORMS. 



A considerable variety of abnormal forms may be produced 

 experimentally in Leptoplana. Duplication of the anterior or 

 posterior end may be obtained by the usual method, viz: partial 

 longitudinal splitting from one end or the other. Repeated cutting 

 of the parts is always necessary in order to obtain duplication and 

 in most cases in spite of all precautions the parts unite, or else the 

 repeated cutting causes the death of the specimen. Since the 

 cephalic ganglia do not regenerate from other parts of the nervous 

 system, duplication of the head is possible only when each part 

 contains a considerable portion of one of the ganglia, /. e., only 

 when the cut lies very near the median plane. Tails can be pro- 

 duced from a cut surface facing more or less posteriorly anywhere 

 along the lateral margin of the body provided the part can be kept 

 from umtmg with the other parts. 



A full description of the various experiments is unnecessary since 

 both method and results are similar to those described for other 

 species of Turbellaria. A few of the experiments, however, are of 

 interest and are given brief consideration. 



I. Formation of a Tail BcHveen Tzvo Heads. 



This specimen was one of a series of ten in which the attempt 

 was made to duplicate the head region by splitting the body from 

 the anterior end along the median line to the pharyngeal region. 

 Five good cases of duplication were obtained, after cutting several 

 times, some with heads of equal size, others with one head 



