No. 4.] 



PLA AVJ RIA MA CL r L A TA . 



201 



of tissue as a whole, so as to give the anterior end a posterior 

 direction, or pseudoheteromorphosis. 



Perhaps the best example of pseudoheteromorphosis is found 

 in Fig. 15, which was produced in the following manner. On 

 Dec. 22, 1898, the worm was operated on by splitting its tail, 

 as indicated by the line a ,in Fig. 13. 

 Then a small anteriorly directed piece of 

 tissue was partly isolated on the inner 

 margin of the right tail b, which developed 

 a head, as seen in Fig.*4, by Jan. 9, 1899. 



Fig. 15 represents the same worm in 

 an expanded condition during locomotion. 



Fig. 1 6 was produced in the same way 

 as Fig. i 5, except that the strip, which was FIG. i S . -The worm of rig. i 4 

 isolated from the inner edge of the right man expanded condition. 



tail, was cut longer, as indicated by the dotted line c in Fig. 13. 

 Neither Van Duyne nor Morgan gives evidence of having 

 produced anything other than pseudoheteromorphosis. 



4. Critique of Evidence. - - In Van Duyne's first example of 

 heteromorphosis (Fig. 3 of the plate) he 

 figures a worm with two heads, one of which 

 arose from the wound caused by taking a 

 piece from its side by two cuts, a transverse 

 one back of the right half, of the head, and 

 a longitudinal one from the inner end of the 

 first cut to the tip of the tail. 



In order that this be an example of axial 

 heteromorphosis it must have been regener- 

 ated from tissue which originally bore the 

 same relation to the main axis of the worm 

 as does the tail, i.e., it must have been re- 

 FIG. 16. - Pseudohetero- generated from tissue, the free end of which 



morphosis. 



was originally posteriorly directed. The 

 drawing does not clearly show this, but rather indicates that 

 this head may have been regenerated on the anterior end of 

 the newly formed tissue on the side of the worm and was 

 forced to turn backward by the shoulder-like projection of old 

 tissue. 



