27 



row and tubular, and distinct from the x-est of the body, a 

 decided angle separating them at the level of the tenta- 

 cles, 



VI. Habits . - One of the most striking habits of the 

 adiilt jelly-fish is its prehensile propensity. The adhe- 

 sive organ at the "knee" of the tentacle is composed of 

 long slender glandular cells, packed into a thick cushion 

 vfiiich is enclosed v/ithin a strongly muscular i-im or collar 

 (Fig. 24). This organ is located on the aboral side of the 

 tentacle(Fig. 25). When at rest the jelly-fish lies on the 

 bottom v/ith inverted bell, and tentacles widely extended 

 horizontally and attached to the bottom by means of the 

 combined vacuum-cup and cement-gland near the tip. How 

 this habit came to be acquired by the adult medusa it is 

 hard to see. But if, as I shall give my reasons for be- 

 lieving, the medusa arises by direct metamorphosis from the 

 hydra, the habits of the hydra would naturally be more or 

 less perrmnent in the adult. It may be that this partic- 

 ular habit is more likely to be first acquired by the larva 

 than by the adult. The tentacles of the hydra reach a rel- 

 ative length greater than in the case of any other known 

 hydroid polyp, I believe. They frequently stretch out in 



