Campanularian Hydroid. 15 



THE MEDUSOID STAGE OF A CAMPANU- 



LARIAN HYDROID. 



General Anatomy. The medusa-buds were observed 

 to be produced asexually along the sides of a specialized 

 hydranth, the blastostyle. If some of the older buds are 

 examined, they will be found to be shaped like an umbrella. 

 The concavity of the umbrella is turned towards the exterior, 

 and the margin is provided with numerous marginal ten- 

 tacles. Stretched across the opening of the umbrella, as a 

 perforate diaphragm, is the so-called velum. The presence 

 of a velum is characteristic of the Hydromedusas and gives 

 to them the name Craspedota. 



By the convex surface the medusa-buds are held to the 

 blastostyle, through which, for a time, they receive their 

 nourishment. When finally mature, the buds break away, 

 and, passing through a terminal opening in the gonangium, 

 reach the sea-water as free-swimming medusae. 1 



If possible, examine a living medusa and note its peculiar 

 movements. How many tentacles are there along the mar- 

 gin of the disc? Do you note a centrally projecting tube, 

 the manubrium? At its free end the mouth is situated. 



1 The terms exumbrella and subumbrella designate the aboral and 

 oral portions respectively. The attachment of the blastostyle is at the 

 aboral or exumbrella portion, while the concavity, surrounded by the" 

 marginal tentacles, is formed by the subumbrella portion. 



