L.M.B.C. MEDUSAE. 383 



the manubrium until the hydra-stage is reached. The 

 tentacles of the posterior verticil first make their appear- 

 ance about 11 to 17 in number, and when they become 

 about 2 mm. long, a second verticil of 8 tentacles appears. 

 The body of the young hydra behind the posterior tentacles 

 becomes covered with a thin perisarc. Sometimes the 

 young hydra breaks away from manubrium before the 

 appearance of the second row of tentacles and remains 

 free in the umbrella cavity. The young hydra with the 

 two verticils of tentacles is about 2 mm. long, and the 

 tentacles of the posterior verticil are a little longer than 

 the body. Often in the same specimen there is an ovum 

 on the manubrium and two or three hydrae showing 

 various stages of development. In a few specimens the 

 asexual budding is taking place at the same time as the 

 sexual reproduction on the manubrium. Sometimes the 

 young medusa on the tentacle-bulb shows also the repro- 

 ductive cells on the manubrium. Several of the young 

 hydroids fixed themselves on the bottom of a glass 

 aquarium, and grew to about 10 mm. in length. A great 

 change took place in the body, which became stem-like and 

 the coenosarc showed longitudinal striae of an orange- 

 red colour. The eight oral tentacles increased slightly 

 in length and the whole head became larger. These 

 hydroids have every appearance of a young Corymorpha. 

 I can see no reason for specifically separating the free- 

 swimming medusae taken by Steenstrup off Iceland and 

 by Sars off Norway from the Port Erin specimens. It is 

 clear from the development of the hydroid of the Manx 

 medusae that the hydroid is not the same as Steenstrup 

 dredged off Iceland. It will be best to leave the Iceland 

 hydroid under the name of Diplura frit ill aria Allmsiu (4), 

 and regard Steenstrup 's free-swimming medusae with two 

 tentacles, and those taken by Sars with one and three 

 tentacles as Ampliicodon fritillaria. 



