MEGAZOOIDAL INDIVIDUALS 95 



observe a similar multiplication of Continuity, within 

 the Individual, in certain humbler forms of life. 



The typical, free-swimming medusiform gonophore is 

 commonly known as a " jellyfish," in company with the 

 truly different Individual Medusa— different not in essential 

 plan, but in Individuality. Its two outstanding structures 

 are the dome, umbrella, or bell, and the club-shaped 

 " manubrium " which hangs from the concavity of this and 

 terminates in a mouth. The bell is more or less transparent, 

 and is largely composed of a jelly-like primitive connective 

 tissue underlying the ectoderm. Near the rim of the bell 

 this connective tissue is replaced by a simple form of 



Fig. 30. — Structure of a free medusiform gonophore. a, Medu- 

 soid (Thaumantias) seen in profile, showing the central polypite, 

 the radiating and circular gonocalycine canals, the marginal 

 vesicles and tentacles, and the reproductive organs ; 6, the 

 same viewed from below. The dotted line indicates the margin 

 of the velum. (Nicholson.) 



muscular tissue which by giving rise to bell contractions 

 causes the megazooid to move gently through the water. 

 From the mouth at the end of the manubrium, or peduncle 

 the alimentary tract runs to beneath the dome of the bell, 

 at which point it divides into, or is continued as four, six, 

 or eight narrow tubes or canals which radiate to the bell- 

 rim as do the ribs of an open umbrella (Fig. 30, a and 6). 



At the bell-rim the radial canals communicate with each 

 other through a circular canal. Thus, the whole canal 

 system is in direct communication with the mouth roughly 

 in the same way as is the chamber system of the sea- 

 anemone. 



It is clear that such a digestive-vascular system as the 



