REPRODUCTION. 



109 



central process, which is known by the name of the " manu- 

 brium." 



The whole organism swims 

 gaily through the water, pro- 

 pelled by the contractions of the 

 bell or disc (gonocalyx) ; and no 

 one would now suspect that it 

 was in any way related to the 

 fixed plant -like zoophyte from 

 which it was originally budded 

 off. The central polypite is fur- 

 nished with a mouth at its distal 

 end, and the mouth opens into a 

 digestive sac. From the proxi- 

 mal end of this stomach proceed 

 four radiating canals which ex- 

 tend to the circumference of the 

 disc, where they all open into a 

 single circular vessel surrounding 

 the mouth of the bell. From the 

 margins of the disc hang also 

 a number of delicate extensile 

 filaments or tentacles ; and the 

 circumference is still further 

 adorned with a series of brightly- 

 coloured spots, which are pro- 

 bably organs of sense. The mouth of the bell is par- 

 tially closed by a delicate transparent membrane or shelf, 

 the so-called "veil." Thus constituted, these beautiful 

 little beings lead an independent and locomotive existence 

 for a longer or shorter period. Ultimately, the essential 

 elements of reproduction are developed in special organs, 

 situated in the course of the radiating canals of the disc. 

 The resulting embryos are ciliated and free-swimming, but 

 ultimately fix themselves, and develop into the plant-like 

 colony from which fresh medusoids may be budded off. 



Fig. 31. Free medusiform gono- 

 phore of Clytia Johnstoni {after 

 Hincks). a. Central polypile or 

 manubrium; b b Radiating gas- 

 tro- vascular canals; c Circular 

 canal; in Marginal bodies; t 

 Tentacles. 



