26 The Irish Naturalist. February, 



the struggle for freedom two or three came off together, and 

 separated afterwards. 



A Scyphistoma in the process of segmentation is known as 

 a Strobila. In the specimen under observation, Ephyrae were 

 liberated three days after the commencement of strobilization. 

 The Ephyrae when first liberated were pinkish, but soon 

 changed to a translucent white. They measured about 2 mm. 

 in diameter. The disc or umbrella was flat and divided into 

 eight marginal lobes, each bearing a sense-organ (tentacu- 

 locyst). The next step was to try the experiment of rearing 

 an Ephyra up to the adult stage, and to see how large the 

 medusa would grow in confinement. On April 17th six 

 Ephyrae, liberated on 3rd and 4th April, were placed in a 

 bell-jar containing some Sarsia tubulosa ; the latter were soon 

 eaten, in spite of their being much larger and more active 

 swimmers. By April 22nd the largest Ephyra was beginning 

 to assume its adult form. 



The umbrella measured half an inch in diameter, and four 

 tentacles had developed on the margin. The tentacles when 

 fully expanded were about 4 inches in length. The circular 

 mouth of the Ephyra was now surrounded by four oral arms. 

 Their food supply consisted chiefly of small medusae, which 

 were greedily devoured. The largest of the Ephyrae 

 (measured on April 22nd) increased in size more rapidly 

 than its companions, and proved itself to be the survivor of the 

 fittest by eating them. On May 16th the survivor measured 

 1^ inches across the umbrella. The oral arms, now frilled, 

 were 2\ inches in length. Four more tentacles had appeared, 

 and others were just visible, one on each side of every sense- 

 organ. 



By May 22nd it had reached the normal form of the adult 

 (just seven weeks old) having 24 marginal tentacles. The 

 umbrella measured 2^ inches in diameter, and the frilled oral 

 arms 5 inches in length. On June 4th the brown markings on 

 the top of the umbrella began to appear. The umbrella now 

 measured 3I inches across, and the oral arms 9 inches. By 

 June 13th it had become too large for its bell-jar (12 inches 

 across and 8 inches deep), so it was removed to another 14 

 inches across and 12 inches in depth, holding when full about 

 4 gallons of water. At this stage the umbrella was 5 inches 





