124 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



regard the whole creature as formed from a 

 Craspedote Medusa which has become mother of a 

 colony and of which the umbrella, developed into 

 the pneumatophore (pn.) has had its radial canals 

 greatly simplified and its tentacles reduced to one 

 during the growth of the colony. The stalk-like 

 stomach (p.) of this medusa has increased in length, 

 but this development is attended by corresponding 

 degeneration, the buccal aperture, which is situated 

 at the free end of the peduncle in normal 

 Craspedote MedusaB, having entirely disappeared. 

 The stalk, formed in this way, serves as a support 

 to the number of other individuals of which the 

 colony is constituted, and which are remarkable 

 for the great morphological variation they exhibit. 

 Among these individuals, those at the top, i.e. 

 those nearest to the air-sac, fulfil the function of 

 locomotion. They become transformed into swim- 

 ming bells (cZ.) and contain no organs whatever. 

 Below these locomotory organs are the sexual 

 individuals, or gonophores (</.), and the sterile 

 individuals (s.). The former are of medusoi'd 

 structure, the umbrella is more or less perfect, and 

 they are sometimes provided with tentacles, and 

 possess a peduncle or manubrium which some- 

 times has a buccal aperture. The sterile individuals 

 provide nutrition for the others. The organs no 

 longer essential to them atrophy in a variable 

 degree. In the case of some the umbrella is 

 present, in others it is absent, and between these 



