BOUGAINVILLIA. 35 



Sections show the same body layers as Hydra, and the 

 derivation of the medusa as an outpocketing of the wall of the 

 hvdranth is evident. 



Hargitt: The Early Development of Penneria tiarolla. Arch f. Entwick- 



lungsmech., 18, 1904. 

 Pearse: Reactions of Tubularia crocea. Am. Nat., 40, 1906. 

 Torrey: Biological Studies on Corymorpha. I. Jour. Exp. Zool., 1, 1904: 



II. Univ. Calif. Pub. Zool., 3, 1907. 



BOUGAINVILLIA. 



This form is not always obtainable during the summer 

 months. It occurs in fair abundance at Woods Hole earlier in 

 the season, attached to piles and floating timbers. 



1. Examine the colony for arrangement of branches, and 

 determine the relation of perisarc and coenosarc. 



2. How do the hydranths differ from those of Obelia? Is 

 the number of tentacles constant? Is the hydranth as contrac- 

 tile as it is in Obelia? 



3. Look for gonosomes. The gonophores are borne singly 

 or in clusters on the main stem and branches. By examining 

 a number of buds the general method of medusa formation can 

 be determined. If possible, find (a) A young bud slightly 

 swollen showing the thin perisarc with the cellular layers inside 

 and a somewhat enlarged ccelenteron. (6) A bud showing a 

 thickening of the ectoderm at the distal end, in which a cavity 

 appears, the sub-umbrellar cavity, (c) A bud showing the 

 formation of the manubrium as a projection into this cavity. 

 The manubrium involves both layers, as the sub-umbrellar 

 cavity is wholly ectodermal. The ectodermal distal covering 

 of the sub-umbrellar cavity will later perforate and form the 

 velum, {d) A bud showing the perforated velum and the 

 tentacles. The tentacles are at first directed through the open- 

 ing of the velum into the sub-umbrellar cavity. 



4. Find medusae that have become detached. Notice the 

 arrangement and number of tentacles, the eye spots at the 

 b^ses of the tentacles, the radial and circular canals, and the 



