DIVISIONS OF THE HYDROZOA. 69 



proceed four radiating canals which extend to the margins of 

 the bell, where they all open into a circular vessel which runs 

 round the mouth of the bell. From the circumference of the 

 bell hang also a number of delicate extensile filaments or 

 tentacles ; and the margin is further adorned with a series of 

 brightly-colored spots, which are probably rudimentary organs 

 of vision and hearing. The mouth of the bell is partially 

 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 ova and sperm-cells are produced 

 in special organs, which are developed in the course of the 

 radiating canals of the disk. The resulting embryos are minute 

 free-swimming bodies, covered with cilia, which finally fix 

 themselves, and develop into the plant-like colonies from which 

 the medusoids were derived. 



