176 



HARDWICKE'S SCIBN CE-GO S S I P. 



up, from observations made this spring, an account 

 of which I think may interest some of the many 

 readers of Science-Gossip. 



Having obtained from a pond a number of Hydra 

 viridis, and wishing, if possible, to witness the pro- 

 duction of this hydra from the ova (which Professor 

 Rymer Jones remarks, in his " Animal Kingdom," 

 has never yet been witnessed), I placed several of 

 them in separate shallow cells, in order to watch the 

 process. This was about the 20th of April, 1S73. 

 All of those thus placed in cells had more or less form- 

 ing upon them at the time the sperm-cells and ovi- 

 sacs, and not a day passed without every one of them 

 being placed under the microscope for examination. 



Fig. ins. Ova of B. viridis, after 

 being hatched out. 



Fig. 106. Ditto before 

 being hatched out. 



If any change had taken place, it was duly noted. I 

 had above thirty eggs altogether distributed in 

 various cells. Some of the ova burst prematurely 

 (as shown in fig. 16, page 13, January number), 

 dispersing their contents in various- sized granules, 

 and finally disappearing. Others gradually shrank 

 up and wasted away ; some of them were destroyed 

 by minute paramecia, that appeared to feed on them. 

 Thus things went on over three weeks, and I began 

 to despair of witnessing the hatcliing-out I so much 

 desired. Still I hoped on, determined not to be beaten 

 if possible. I continued to watch very narrowly from 

 day to day the eggs still left, and on May 22, in one 

 of the eggs from a hydra I had placed in a cell on 

 April 22, I thought I saw a movement in a part 

 of the egg that had become partially clear— as tliey 

 are otherwise all opaque, and their surface, when 

 seen under the microscope, appears to be covered 

 by an irregular network, which is more plainly seen 

 after the hydra has left it (as shown at fig. 105). To 

 make sure, I watched it every hour, and I was not 

 deceived : the minute creature was there, and en- 

 deavouring to liberate itself from the egg ; and, as 

 is characteristic of the hydra, it continued to con- 

 tract and extend its body, until at length the egg, 

 which was perfectly round (as at fig. 106) until 

 now, had, by these exertions, become somewhat 

 elongated, and at the same time thin, so that the 

 object within could be distinctly seen. At times 

 it drew itself up into a complete ball, then again 

 extended itself to its utmost length, thus pressing 

 the egg out until it finally gave way. Just before 

 this took place, while in the egg, two very small 

 tentacles were visible. They were very small in- 

 deed, but still, by their being present, I was enabled 



to distinguish which was the head. After the rup- 

 ture of the egg, which took place thirty-two days 

 after it was laid, I saw the hydra clear itself entirely 

 from it. This took about thirty minutes to accom- 

 plish, from the time of the first perceptible crack or 

 break in the egg ; the young hydra still continuing 

 the contracting and elongating process of its body 

 as before observed while in the egg, and three hours 

 after leaving the egg it presented alternately the 

 forms as in figs. 107 and 108. About the fifth day 



Fig. 107. H, viridis, three hours after 

 leaving the egg (elongated). 



Fig. lOS. Ditto 

 (contracted). 



from the time of hatching, the third tentacle began 

 to show, and on the seventh day the three tentacles 

 were seen, as at fig. 109. It was now observed 

 for the first time to use the suctorial disc on the 

 footstalk, which had been gradually forming, by 

 which it could fix itself to any object. The first 

 few days it appeared to be 

 quite free in the water, still 

 having the power of lengthen- 

 ing and contracting the body ; 

 but when attached by the 

 sucker at the foot, it extended 

 the body to nearly double the 

 length, and the tentacles in- 

 creased in length. What it 

 has fed on since its escape 

 from the egg I cannot say. I 

 could not perceive that it 

 took any food, still it con- 

 tinued to grow slowly. At 

 first it was slightly tinted 

 with green, which gradually 

 became darker, and the colour 

 extended to the tentacles, 

 which at first were quite co- 

 lourless. The eggs vary a little 

 in size, but their mean diameter is about i5Vtb of 

 an inch. Although I have had a large number of 

 hydras during the last three years ^inder observa- 

 tion, I never but once saw two ova produced from 

 one hydra. This, I think, is a rare occurrence, so I 

 now give a sketch of it in fig. 110. 



It has been generally thought and expressed that 

 the Hydra vulgaris deposits its ova in the autumn, 

 and that they are hatched out in the following 



Fig. 109. 



Young Hydra, seven 



days after leaving 



tlie egg. 



