570 



POLYZOA. 



Loxosoma, and is interpreted by Harnier as tlie rudiment of the 

 supraoesophageal ganglion ; it is connected by two nervous tra,cts 

 round the oesophagus with the persistent ganglion, which probably 

 develops from the floor of the vestibule between the mouth and 

 anus as a thickening of ectoderm, and on the same view may be 

 interpreted as the suboesophageal ganglion. 



As was first made known by the independent researches of Barrois 

 and Harmer, the larva fixes itself by the oral surface and then 



KK;. 405. Three stages in the metamorphosis of Pcdicdlina (after Harnier, from Korschelt 

 and Heider). A, just fixed larva. B, beginning of the rotation of the alimentary canal, 

 and disappearance of larval organs. C, formation of new opening of vestibule and of 

 tentacles, a anus ; d dorsal organ ; m mouth ; p gland of attaching surface ; ( rudiments 

 of tentacles ; u> ciliated disc. 



proceeds to undergo the following metamorphosis (Fig. 455). The 

 opening of the vestibule closes, the dorsal organ and apical plate 

 disappear, and the alimentary canal apparently undergoes a process 

 of rotation of such a kind that the atrium comes to lie on the 

 surface opposite to that by which the animal is attached. Mean- 

 while a stalk is formed by the elongation of the new aboral region, 



