HAKDWICKE'S SCIENCE-GOSSIP. 



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a number of Hydras in my aquarium had become 

 b'.udded with white liemispherical-sbaped Jumps, 

 rather prominently raised in the centre (as sliown 

 in iig. O-l, a), I took some of them out of the water, 

 and examined them under the microscope in a shal- 

 low cell ; when I observed in the extreme tips of 

 those lumps a number of moving objects, having the 

 appearance of so many minute animalcules, which 

 kept up continual and rapid movements. After a 



Fig. 9J. Hytlra, s-howing iirominences a, and b eruptions. 



lime, I distinctly saw an eruption of some of those 

 protuberances, and springing out from them, with 

 considerable force, a number of those moving ob- 

 jects (fig. 9t, d), which appeared to disperse them- 

 selves in the water around the Hydra. At that 

 time the Hydra did not take food, and the tentacles 

 gradually contracted, and finally the whole body 

 dissolved into a confused mass of whitish granules. 

 Now the question arose in my mind as to what 

 these living moving things could be that occupied 

 Ihekrnpsand finally escaped into the water sur- 

 rounding the body of the Hydra, Were they the 



spermatozoa escaping from the sperm-cells fertiliz- 

 ing the ova in the ovi-sacs ? Both the sperm-cells 

 and ovi-sacs are to be found on the same polyp, and 

 at its final dissolution the ovum sinks t,o the bottom 

 and lies hidden in the mud, from which ovum the 

 Hydra is reproduced in the following spring. This 

 appears to me to be the case, and though this 

 manner of the formation of the Hydras from ova 

 has never been traced or witnessed, yet I think we 

 have reason to conclude that this is tlic fact, as after 

 the disappearance of the Hydras in the autumn, 1 

 have during the winter closely examined the water 

 and plants growing in it, and have not been able to 

 find one single Hydra; and then again in the spring, 

 I have observed a very icw small ones indeed, and 

 after a time have found them increasing by gemma- 

 tion or budding, which is tlie usual manner of their 



Fig-. 95. rirst stage in ilcvelopmcnt of Hydra. 



propagation during the summer months. All this 

 can be witnessed by any one during the summer 

 by keeping them in a small aquarium under obser- 

 vation. The reason why I think the small Hydras 

 that make their appearance first in the spring are 

 produced from ova is the fact that, ^vhen produced 

 by budding, I have always observed that the young 



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Fig. g6. Second stage in development of Hj dra. 



on:s do not leave the parent stem until they are 

 fuUgrown, and as large as the parent itself; and 

 even sometimes a bud is seen on the young one be- 

 fore it leaves the parent stem. So I conclude that 

 those very small ones which fiist appear are pro- 



