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POPULAR SCIENCE REVIEW. 
EXPLANATION OF PLATE. 
Fig. 1. Portion of duckweed ( Lemna ) with Hydrae attached. 
„ 2. Magnified specimen of H. vulgaris , showing spermigerous capsules 
at a, and ovigerous capsule at &.* 
„ 3. Ova of Hydra with polypes coming out therefrom. Magnified. 
„ 4. Spermigerous capsule burst under pressure, exhibiting spermatozoa. 
Magnified. 
„ 5. Magnified representation of a ruptured ovum. 
„ 6. Sarcodic globule from a hydra’s tentacle, in which is imbedded one of 
the so-called stinging organs, the spines and filament inclosed. 
„ 7. The Cnida, or thread-cell, with spines and filaments protruded. All 
highly magnified. 
„ 8. A specimen of Hydra fusca attached to a piece of stick. Natural size. 
„ 9. Eepresents some of the results which Trembley obtained by inserting 
one polype within another. The tail end of the interior animal is 
seen to be pushing itself out of the exterior polype at b ; c and cl, 
the same animals, with young, subsequently formed, attached, e 
is a polype which, after having been turned inside out and cut with 
a pair of scissors, at the end of two months was of the shape repre- 
sented in the figure. 
„ 10. A parasite, common on Hydra viridis , called Trichodina pediculus. 
Magnified about 300 diam. 
* By an error the tentacles have been represented as possessing cilia. 
