No. 5.] VARIATION AMONG HYDROMEDUSAE. 235 



primary canals, which divided the bell into approximately pen- 

 tamerous segments, as shown in PI. Ill, Fig. 12. In another 

 there was a very evident forking of two of the four primary 

 canals, as shown in PI. Ill, Fig. 9 ; for while the bell was 

 divided into hexamerous segments, the manubrium was sym- 

 metrically tetramerous. In every one of the other five hexam- 

 erous specimens the canals converged at the aboral pole in a 

 perfectly symmetrical way, though the hexamerism extended 

 to the manubrium in only two specimens, and in these only 



FK,. 9. Hexamerous specimen showing pentamerous stomach and varying size and 



distribution of tentacles. 



the basal portion or gastric pouch was strictly hexamerous. In 

 at least two other of these hexamerous specimens the oral 

 lobes of the manubrium were four (cf. Fig. 9). 



Of specimens having three and five canals there were by far 

 the larger number, with the preponderance slightly in favor of 

 the trimerous variety, but not sufficiently so to warrant any 

 conclusions as to the question whether the course of variation 

 was toward a trimerous rather than a pentamerous condition. 

 Of those with three canals there were twenty-one specimens, 

 while of those with five there were eighteen specimens. Of 

 those making up the total of seventy-two specimens there were 



