158 MICROSCOPY FOR BEGINNERS. 



They never eat any but animal food, and they are al- 

 ways hungry. 



The body and tentacles of Hydra mridis are rough- 

 ened by little elevations or warty prominences. The 

 brown species (II. fused) is not so much roughened. 

 These warts contain what are called the stings. These 

 are smajl oval or vase-shaped hollow bodies, with a fine 

 thread coiled in the interior, and four minute spines 

 near the summit. When the Hydra is irri- 

 tated by the pressure of the cover-glass these 

 stings are thrown out violently, and the long 

 stiff thread can be well seen. When in the 

 animal's body they cannot be easily examined. 

 One is shown much magnified in Fig. 130<z. 

 Fig. isoo. They are often found on the slide when no 



Hydra sting. . 



Hydra is to be seen, and they are sometimes 

 noticeable sticking in the body of some worm or larva 

 that has escaped a fatal embrace. I have more than 

 once found a Chironomus larva (Chapter VII.) in a 

 dying condition and ornamented by a spiral band of 

 these stings in its skin, it having evidently had a tussle 

 with a Hydra and escaped. 



The Hydra increases in numbers rapidly by a process 

 of budding. A little protuberance appears on one side 

 of the body, enlarging and growing, and finally, while 

 still attached to the parent, developing tentacles, then 

 resembling the mature animal in everything except size. 

 And it is not unusual to see one or more still younger 

 Hydras sprouting from these before they are free from 



