374 EVENINGS AT THE MICROSCOPE 



tractile force behind; while we see the fluids, carrying 

 granules, run into the parts of the tentacles which are 

 already free. The embryo is liberated. 



" For a few seconds it appears helpless, and falls through 

 the water in a collapsed state, so that we cannot discern 

 its proper form. It gives a spasmodic contraction or two, 

 feeble at first, then more vigorous; the tentacles lengthen, 

 the body expands, and lo! it is not a Polype, but a 

 Medusa ! 



And now take your eye for a moment from the micro- 

 scope, and glance at this glass jar, in which the Oarweed 

 with its colony of Zoophytes has been standing for a few 

 hours. Hold it between your eye and the light; do you 

 not see that the water is alive with tiny dancing atoms ? 

 Hundreds are there, playing and pumping through the 

 fluid with a sort of flapping motion, which, when you 

 get on sidewise in clear view, will not fail to remind you 

 of the flagging flight of some heavy-bodied, long- winged 

 bird. These are the Medusa-shaped progeny of the Lao- 

 medea. 



But let us return to the one of which we have just 

 witnessed the birth, and which is still flapping to and fro 

 in the narrow glass trough. You see a pellucid colorless 

 disk or umbrella of considerable thickness, about one-six- 

 tieth of an inch in diameter in its average state of expan- 

 sion. Its substance has a reticular appearance, probably 

 indicating its cellular texture. Internally, the disk rises 

 to a blunt point in the centre, whence four vessels diverge 

 to opposite points of the margin. These form elevated 

 ribs, the surface being gradually depressed from each to 

 the centre of the interspace. Externally, the centre of the 

 disk is produced into a fleshy peduncle, having a narrow 



