194 LEMOX. [VOL. I. 



eight pieces as nearly equal in size as possible. All pieces 

 regenerated lost parts and became fully developed worms in 

 about ten days at ordinary room temperature. _ Another worm 

 5 mm. long and i mm. wide was cut into eight pieces. The 

 operation was, however, so delicate that there was not much 

 certainty in obtaining uniform size of the pieces. The larger 

 pieces regenerated the lost organs, while the smaller ones did 

 not. Just what the limit is, was hard to ascertain, as the rela- 

 tion of the piece to the whole could not be accurately deter- 

 mined, on account of its constantly varying shape. Parts 

 which, by the most careful measurements, were shown to be 

 about one-twelfth of the size of the original animal, regener- 

 ated and became fully formed planarians, while those of smaller 

 size did not. Experiments on sixteen worms resulted in the 

 same way. The area in front of the eyes did not regenerate 

 in a single case. 



2. Production of Compound Planarians. - -This may be 

 brought about in two ways : (i) Parts separated by cuts made 

 along or near the middle line will generally complete them- 

 selves by regeneration without much growth. (2) Even 

 extremely minute strips partly isolated may grow out like 

 buds, and when of sufficient size, develop the characteristic 

 organs of the species. 



There is, of course, no line of demarcation between these 

 two ways, which are united by a series of intermediates. 



a. By Regeneration. - -When a worm was split through the 

 middle line of the anterior part of the body, sometimes the 

 partly isolated left half regenerated a new right half and 

 the partly isolated right half a new left half, thus producing a 

 worm with two complete heads (Fig. i). A similar operation 

 may be performed on the posterior part of the body, resulting 

 in two tails (Fig. 2). The time required for the regeneration 

 of two heads is fifteen to twenty days, varying somewhat 

 according to temperature. The regeneration of double tails 

 occurred in five to ten clays. 



On Dec. 24, 1898, a large planarian was operated on by 

 splitting the tail, as indicated in Fig. 13, except that the cut 

 did not extend through the pharynx but only to the region 



