Pressure upon the Regeneration o/'Gunda ulvse. 9 



of parenchyma cells, one parenchyma cell forming one differentiated 

 muscle fibre (fig. 7). The restoration of the circle of the nerve cords also 

 takes place by parenchyma cells pushing their way into the cut end of 

 the old nerve cords and becoming transformed into nerve cells. The new- 

 gut is formed by the cut ends of the two branches of the old gut fusing 

 together behind the pharynx. The wound on the pharynx is also healed 

 by the migration of parenchyma cells. 



The new mouth is formed by a perforation appearing between the pharynx 

 chamber and the exterior. The mouth perforates at a point just anterior to 

 the point of closure of the wound, usually about nine days after section 

 (fig. 7, m. and w.\ 



While the constructive changes described above have been taking place 

 in the region of the wound, in the rest of the animal's body reductive change 

 has been simultaneously proceeding. The first system to show degenerative 

 change is the generative system. The amount of degeneration that takes 

 place is directly proportional to the amount of restoration that is required. 

 In the present case, where regeneration is being considered after a cut that 

 has removed half the body, reduction proceeds so far that the whole of the 

 generative system is absorbed. The yolk glands are absorbed first, then the 

 genital glands and secondary sexual organs. 



Besides the absorption of the genital system it can be seen on referring to 

 figs. 5, 1-4, and 8, 1-4, that the growth in size of the posterior end is 

 accompanied by a reduction in size of the anterior end. This external 

 adjustment is found to apply also to all the internal organs of the animal, 

 i.e., as the new parts grow larger the old grow smaller until the proper 

 equilibrium is reached. 



When these changes have restored the normal proportions of the worm, 

 regulation is complete. The subsequent increase in size, and in the case 

 under consideration, restoration of the generative system, are phenomena of 

 normal growth (see Section II, b). 



It might here be noticed that the reductional changes described above in a 

 regenerating worm fragment are entirely identical with those described in 

 Part II (a) of this paper, where the reduction was the result of starving whole 

 animals. It will be seen later that, when regeneration is inhibited, reduction 

 is inhibited to the same degree. Absorption of the generative system takes 

 10 weeks in starving worms ; in animals which have been bisected and are 

 regenerating under starving conditions it takes 5-6 weeks. In animals 

 which have been bisected and are being fed while regenerating, the genital 

 system is greatly reduced, but never completely absorbed. 



