TEE HYDRA AND JELLY-FISH. 



29 



masses on the reefs of Florida and the Pacific Ocean. The 

 name is derived from the numberless 

 minute holes or pores scattered over the 

 surface in which the nutritive (Fig. 23, 

 a) and tentaculated zooids (Fig. 23, b) 

 live. On breaking off pieces of the living 

 coral one's hand is stung and made sore 

 for days by the stings from the lasso-cells 

 (Fig. 23, c, d, e), so poisonous is this 

 coral-like growth. 

 A common Hydroid on our northern 



shores is the Coryne 



(Fig. 24), which differs 



from the foregoing kinds FlG . S4 ._ The polyp of Co . 



in producing a free bell- ryne mirabUis, with a 

 ,.-, ,, medusa-bud at a. (Much 



like form called a me- enlarged.) 

 dusa, or jelly-fish (Fig. 25). Most jelly-fishes 

 are more or less bell or umbrella-shaped, and 

 are delicate transparent creatures which move 

 about in the water, by opening and closing 

 the edge of the disk-like body. From the 

 centre of the body hangs down a hollow pro- 

 boscis-like tube, the stomach, from the base 

 of which radiate four canals or passages which 

 open into a circular passage around the edge 

 of the disk. This is the water-vascular 

 system, and the fluid it contains is sea- 

 water mixed with the digestive fluid; this 

 fluid thus rudely corresponds to the blood of 

 higher animals. Four long thread-like ten- 

 tacles in the Coryne hang down from the 

 edge of the disk. These delicate jelly-fishes 

 FIG. 25. Free Me- possess a nervous ring passing around the 



dusa of Coryne, n ,-, ,. , 11 -, -,-, 



with the four edge oi the disk, and also eyes and usually 

 (Enfarged. ^ c es ' ears situated at intervals on the edge of the 



disk. We thus find for the first time a true nervous 



system. 



