No. 4.] 



PLA NA RIA MA CULATA. 



'95 



just posterior to it. On Jan. 3, 1899, two fully f rme d tails 

 had developed. On January 5, the animal divided by fission 

 about 3 mm. in front of the point of union of the two tails. 

 The part possessing the two tails regenerated a new head, pro- 

 ducing the animal seen in Fig. 3. 



On January 1 1, the anterior part of the worm was again split 

 posteriorly, this time dividing the pharynx. Five days later, on 

 January 16, the posterior end of the worm again divided off, 

 and subsequently regenerated a new head, as seen in Fig. 4. 

 The third and most anterior part of the original 

 worm was split posteriorly, but the double tails 



FIG. 



FIG. 2. 



FIG. 3. 



FIG. 4. 



FIG. 5. 



FIG. i. A double-headed planarian caused by regeneration after the original head had been split. 

 FIG. 2. A planarian with two tails resulting from splitting and regeneration. 

 FIG. 3. A planarian which separated from that of Fig. 5 by fission after its tail had been split. 

 FIG. 4. This worm also separated from that of Fig. 5 by fission eleven days after Fig. 3. 

 FIG. 5. -The head end of the worm from which those in Figs. 3 and 4 separated. 



could not be produced again, although the operation was per- 

 formed three times. The only result that could be obtained was 

 a worm with a slightly bifid tail and double pharynx (Fig. 5). 



An interesting feature of the experiment with this worm is 

 the way in which the alimentary canal developed in the regen- 

 erated parts. The left tail of Fig. 3 is supplied with nutriment 

 by means of a sub-branch which comes off from the anterior 

 branch of the canal, while the original left branch of the canal, 

 which was severed in the operation, has disappeared. On the 

 other hand, the right tail of Fig. 4 receives its nutriment by a 

 sub-branch from the right posterior branch of the canal, which 

 still persists, or is possibly a new formation. This and other 

 problems concerning the anatomy of compound planarians are 

 of interest and should be worked out. 



