centre of the cross there is attached the large central vesi- 

 cle. In a living specimen 11 cm. in diameter this measured 

 3 cm. in length. There are four other vesicles that most near- 

 ly approach the central one in size and these arise from the 

 arms of the cross near the junntion of the brachial canals. 

 In full >^:rom\ individuals there are eight more vesicles, a lit-^ 

 tie smaller, one on each canal distal to the junction. It 

 is only near the periphery of the disk that the canals are pro- 

 vided with oral funnels. For most of their course on the disk, 

 the canals give rise to the very small vesicles finely speckled 

 with a reddish brown pigment that have already been mentioned. 

 These have nettle batteries at their tips and are so numerous 

 as to completely cover the greater part of tlie disk and to hide' 

 the course of the canals. This mass of small vesicles is not 

 acquired, ho>v ever, until late. Specimens as much as 6 cm. in 

 diameter will be found to be without them. In such specimens 

 we have the five largest vesicles and a number of oral funnels 

 are scattered along the canals just as tliey are upon the arms. 



The Sub^enital Cavities and the Digestive Tract. 

 At each of the four points of junction of the brachial can- 

 als there is a si it-like passage dipping vertically into the 

 jelly of the disk and opening into the stomach. This is a 

 lens-shaped cavity. It has a gently arched roof and its floor 



- 17 - I 



