64 Charles Zeleny. 



The relation of the developing opercula and branchiae of each 

 side to the nerve cord of that side is very interesting. This is most 

 noticeable in the regeneration of these organs from a cut near the 

 posterior end of the thorax M^here the nerve cords are widely 

 separated. In the Serpulidae it will be remembered the nerve 

 cords do not come together ventrally as in most Annelids but 

 remain widely separated, forming two latero-ventral trunks. The 

 principal blood vessels, however, do not have this arrangement. 

 The branchial circlets, each with its operculum, regenerating from 

 a cut near the posterior end of the thorax, are always widely sepa- 

 rated and seem to be located in intimate relation with the nerve 

 trunks of the corresponding sides. This fact agrees very well with 

 the data as made out by Morgan ('02) for the regeneration of the 

 head of the earthworm which showed that the regenerating head 

 always develops in connection with the anterior cut end of the 

 nerve cord. A similar relation has been made out for other forms. 

 A further discussion of this and other cases of nervous control in 

 regeneration is reserved for a future time. 



The results of a transverse cut in the abdominal region were in 

 every case negative as far as the posterior piece is concerned. Its 

 anterior cut surface in every case healed over and no regeneration 

 took place. The piece lived for a considerable time but did not 

 show any signs of regenerating tissue. 



In this connection two other groups of experiments may be 

 described. 



The first concerns the regeneration and regulation following 

 the longitudinal dorso-ventral division of the body into equal right 

 and left parts. 



In this group a dorso-ventral longitudinal cut divided the body 

 into approximately equal right and left halves. Fourteen speci- 

 mens were operated on in this way and of these several showed 

 traces of the regeneration of knob-like elevations near the anterior 

 end of the cut surface. Two of these showed especially clear 

 structures which correspond very well with young regenerating 

 branchial circlets from the anterior end of a posterior piece after 

 transverse section of the thorax. It is probable that the new 

 structures may be located at a cut end of a nerve cord. In one 

 of the cases the new circlet in question was a considerable dis- 

 tance behind the old branchial circlet. In no case did the animal 

 live long enough to allow of a full development of the new organs. 



