RECONSTITUTIONAL PATTERNS IN EXPERIMENT 



385 



versal of host polarity and reorganization of digestive tract. After re- 

 moval of the anterior region of the host at A' A', following development of 

 the reversed pharynx, head regeneration was inhibited. In Figure 129, 

 E and F, is shown a case of complete re- 

 versal of host polarity and also reversal 

 in the graft, because it was given a pos- 

 terior free surface after union, by remov- 

 al of regions posterior to it. In G and H 

 a pharynx is induced both posterior and 

 anterior to the graft, and later removal 

 of the host anterior end is followed by 

 development of a posterior end instead 

 of a head. In / polarity of the graft is 

 altered go° because its free surface, from 

 which the head develops, was originally 

 lateral, a pharynx is induced posteriorly, 

 and later section of the host at A' A' is 

 followed by induction of another pharynx 

 at a host-level originally anterior to the 

 graft-level and development of a posterior 

 end from the originally anterior cut sur- 

 face (/). 



Ganglionic grafts in the posterior zooid 

 region very generally induce a postce- 

 phalic outgrowth and reorganization of 

 the host body posterior and for a certain 

 distance anterior to the graft. Two ex- 

 amples are shown in Figure 130, and 

 others with heteroplastic grafts and show- 

 ing reorganization of the digestive tract 

 in Figure 131. A and B show induction 

 in both directions, though the graft head 

 is far from normal in both; C is the poste- 

 rior product of fission following induction 

 by the graft both posteriorly and anteriorly, with development of posterior 

 end instead of head from the originally anterior surface of fission {A). In 

 this individual gradual fusion of the two posterior ends resulted in the con- 

 dition of Figure 131, /), with two pharynges at the same body-level and 

 with a duplicated postpharyngeal digestive tract. Later fissions in cases 



Fig. 130, A, B. — Induction by gan- 

 glionic grafts in posterior zooid region. 

 A, homoplastic, Diigesia tigrina novan- 

 gliae; induced postcephalic tubular out- 

 growth and reorganization of host body 

 with development of pharynx posterior 

 and anterior to the graft-level. B, het- 

 eroplastic, D. tigrina novangliae to D. 

 dorolocephala; induction by graft of 

 postcephalic outgrowth and of reor- 

 ganization of host with pharynx de- 

 velopment posterior and anterior to 

 graft-level (from Santos, 1929, 1931). 



